diff --git a/src/Twilio/Rest/Assistants/V1/Assistant/FeedbackModels.php b/src/Twilio/Rest/Assistants/V1/Assistant/FeedbackModels.php
index 0cef87598..c90f1c649 100644
--- a/src/Twilio/Rest/Assistants/V1/Assistant/FeedbackModels.php
+++ b/src/Twilio/Rest/Assistants/V1/Assistant/FeedbackModels.php
@@ -57,12 +57,19 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'message_id' => $this->messageId,
-            'score' => $this->score,
-            'session_id' => $this->sessionId,
-            'text' => $this->text
+        $jsonString = [
+            'session_id' => $this->sessionId
         ];
+        if (isset($this->messageId)) {
+            $jsonString['message_id'] = $this->messageId;
+        }
+        if (isset($this->score)) {
+            $jsonString['score'] = $this->score;
+        }
+        if (isset($this->text)) {
+            $jsonString['text'] = $this->text;
+        }
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/Assistants/V1/Assistant/MessageModels.php b/src/Twilio/Rest/Assistants/V1/Assistant/MessageModels.php
index 06e040d67..87d1be9eb 100644
--- a/src/Twilio/Rest/Assistants/V1/Assistant/MessageModels.php
+++ b/src/Twilio/Rest/Assistants/V1/Assistant/MessageModels.php
@@ -61,13 +61,20 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'identity' => $this->identity,
-            'session_id' => $this->sessionId,
-            'body' => $this->body,
-            'webhook' => $this->webhook,
-            'mode' => $this->mode
+            'body' => $this->body
         ];
+        if (isset($this->sessionId)) {
+            $jsonString['session_id'] = $this->sessionId;
+        }
+        if (isset($this->webhook)) {
+            $jsonString['webhook'] = $this->webhook;
+        }
+        if (isset($this->mode)) {
+            $jsonString['mode'] = $this->mode;
+        }
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/Assistants/V1/AssistantModels.php b/src/Twilio/Rest/Assistants/V1/AssistantModels.php
index c562988c1..4ab89ab53 100644
--- a/src/Twilio/Rest/Assistants/V1/AssistantModels.php
+++ b/src/Twilio/Rest/Assistants/V1/AssistantModels.php
@@ -83,10 +83,11 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'perception_engine_enabled' => $this->perceptionEngineEnabled,
             'personalization_engine_enabled' => $this->personalizationEngineEnabled
         ];
+        return $jsonString;
     }
 }
 
@@ -113,11 +114,18 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'profile_api_key' => $this->profileApiKey,
-            'space_id' => $this->spaceId,
-            'write_key' => $this->writeKey
+        $jsonString = [
         ];
+        if (isset($this->profileApiKey)) {
+            $jsonString['profile_api_key'] = $this->profileApiKey;
+        }
+        if (isset($this->spaceId)) {
+            $jsonString['space_id'] = $this->spaceId;
+        }
+        if (isset($this->writeKey)) {
+            $jsonString['write_key'] = $this->writeKey;
+        }
+        return $jsonString;
     }
 }
 
@@ -150,13 +158,22 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'customer_ai' => $this->customerAi,
-            'name' => $this->name,
-            'owner' => $this->owner,
-            'personality_prompt' => $this->personalityPrompt,
-            'segment_credential' => $this->segmentCredential
+        $jsonString = [
+            'name' => $this->name
         ];
+        if (isset($this->customerAi)) {
+            $jsonString['customer_ai'] = $this->customerAi;
+        }
+        if (isset($this->owner)) {
+            $jsonString['owner'] = $this->owner;
+        }
+        if (isset($this->personalityPrompt)) {
+            $jsonString['personality_prompt'] = $this->personalityPrompt;
+        }
+        if (isset($this->segmentCredential)) {
+            $jsonString['segment_credential'] = $this->segmentCredential;
+        }
+        return $jsonString;
     }
 }
 
@@ -189,13 +206,24 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'customer_ai' => $this->customerAi,
-            'name' => $this->name,
-            'owner' => $this->owner,
-            'personality_prompt' => $this->personalityPrompt,
-            'segment_credential' => $this->segmentCredential
+        $jsonString = [
         ];
+        if (isset($this->customerAi)) {
+            $jsonString['customer_ai'] = $this->customerAi;
+        }
+        if (isset($this->name)) {
+            $jsonString['name'] = $this->name;
+        }
+        if (isset($this->owner)) {
+            $jsonString['owner'] = $this->owner;
+        }
+        if (isset($this->personalityPrompt)) {
+            $jsonString['personality_prompt'] = $this->personalityPrompt;
+        }
+        if (isset($this->segmentCredential)) {
+            $jsonString['segment_credential'] = $this->segmentCredential;
+        }
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/Assistants/V1/KnowledgeModels.php b/src/Twilio/Rest/Assistants/V1/KnowledgeModels.php
index e4ec4e2cb..f5e06962a 100644
--- a/src/Twilio/Rest/Assistants/V1/KnowledgeModels.php
+++ b/src/Twilio/Rest/Assistants/V1/KnowledgeModels.php
@@ -88,13 +88,22 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'description' => $this->description,
-            'id' => $this->id,
-            'name' => $this->name,
-            'policy_details' => $this->policyDetails,
-            'type' => $this->type
+        $jsonString = [
+            'policy_details' => $this->policyDetails
         ];
+        if (isset($this->description)) {
+            $jsonString['description'] = $this->description;
+        }
+        if (isset($this->id)) {
+            $jsonString['id'] = $this->id;
+        }
+        if (isset($this->name)) {
+            $jsonString['name'] = $this->name;
+        }
+        if (isset($this->type)) {
+            $jsonString['type'] = $this->type;
+        }
+        return $jsonString;
     }
 }
 
@@ -133,15 +142,26 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'assistant_id' => $this->assistantId,
-            'description' => $this->description,
-            'knowledge_source_details' => $this->knowledgeSourceDetails,
+        $jsonString = [
             'name' => $this->name,
-            'policy' => $this->policy,
-            'type' => $this->type,
-            'embedding_model' => $this->embeddingModel
+            'type' => $this->type
         ];
+        if (isset($this->assistantId)) {
+            $jsonString['assistant_id'] = $this->assistantId;
+        }
+        if (isset($this->description)) {
+            $jsonString['description'] = $this->description;
+        }
+        if (isset($this->knowledgeSourceDetails)) {
+            $jsonString['knowledge_source_details'] = $this->knowledgeSourceDetails;
+        }
+        if (isset($this->policy)) {
+            $jsonString['policy'] = $this->policy;
+        }
+        if (isset($this->embeddingModel)) {
+            $jsonString['embedding_model'] = $this->embeddingModel;
+        }
+        return $jsonString;
     }
 }
 
@@ -177,14 +197,27 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'description' => $this->description,
-            'knowledge_source_details' => $this->knowledgeSourceDetails,
-            'name' => $this->name,
-            'policy' => $this->policy,
-            'type' => $this->type,
-            'embedding_model' => $this->embeddingModel
+        $jsonString = [
         ];
+        if (isset($this->description)) {
+            $jsonString['description'] = $this->description;
+        }
+        if (isset($this->knowledgeSourceDetails)) {
+            $jsonString['knowledge_source_details'] = $this->knowledgeSourceDetails;
+        }
+        if (isset($this->name)) {
+            $jsonString['name'] = $this->name;
+        }
+        if (isset($this->policy)) {
+            $jsonString['policy'] = $this->policy;
+        }
+        if (isset($this->type)) {
+            $jsonString['type'] = $this->type;
+        }
+        if (isset($this->embeddingModel)) {
+            $jsonString['embedding_model'] = $this->embeddingModel;
+        }
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/Assistants/V1/ToolModels.php b/src/Twilio/Rest/Assistants/V1/ToolModels.php
index 58e27f227..42a83cdf0 100644
--- a/src/Twilio/Rest/Assistants/V1/ToolModels.php
+++ b/src/Twilio/Rest/Assistants/V1/ToolModels.php
@@ -89,13 +89,22 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'description' => $this->description,
-            'id' => $this->id,
-            'name' => $this->name,
-            'policy_details' => $this->policyDetails,
-            'type' => $this->type
+        $jsonString = [
+            'policy_details' => $this->policyDetails
         ];
+        if (isset($this->description)) {
+            $jsonString['description'] = $this->description;
+        }
+        if (isset($this->id)) {
+            $jsonString['id'] = $this->id;
+        }
+        if (isset($this->name)) {
+            $jsonString['name'] = $this->name;
+        }
+        if (isset($this->type)) {
+            $jsonString['type'] = $this->type;
+        }
+        return $jsonString;
     }
 }
 
@@ -134,15 +143,24 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'assistant_id' => $this->assistantId,
-            'description' => $this->description,
+        $jsonString = [
             'enabled' => $this->enabled,
-            'meta' => $this->meta,
             'name' => $this->name,
-            'policy' => $this->policy,
             'type' => $this->type
         ];
+        if (isset($this->assistantId)) {
+            $jsonString['assistant_id'] = $this->assistantId;
+        }
+        if (isset($this->description)) {
+            $jsonString['description'] = $this->description;
+        }
+        if (isset($this->meta)) {
+            $jsonString['meta'] = $this->meta;
+        }
+        if (isset($this->policy)) {
+            $jsonString['policy'] = $this->policy;
+        }
+        return $jsonString;
     }
 }
 
@@ -181,15 +199,30 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'assistant_id' => $this->assistantId,
-            'description' => $this->description,
-            'enabled' => $this->enabled,
-            'meta' => $this->meta,
-            'name' => $this->name,
-            'policy' => $this->policy,
-            'type' => $this->type
+        $jsonString = [
         ];
+        if (isset($this->assistantId)) {
+            $jsonString['assistant_id'] = $this->assistantId;
+        }
+        if (isset($this->description)) {
+            $jsonString['description'] = $this->description;
+        }
+        if (isset($this->enabled)) {
+            $jsonString['enabled'] = $this->enabled;
+        }
+        if (isset($this->meta)) {
+            $jsonString['meta'] = $this->meta;
+        }
+        if (isset($this->name)) {
+            $jsonString['name'] = $this->name;
+        }
+        if (isset($this->policy)) {
+            $jsonString['policy'] = $this->policy;
+        }
+        if (isset($this->type)) {
+            $jsonString['type'] = $this->type;
+        }
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/Content/V1/Content/ApprovalCreateModels.php b/src/Twilio/Rest/Content/V1/Content/ApprovalCreateModels.php
index c1581bb6a..5ea38d107 100644
--- a/src/Twilio/Rest/Content/V1/Content/ApprovalCreateModels.php
+++ b/src/Twilio/Rest/Content/V1/Content/ApprovalCreateModels.php
@@ -49,10 +49,11 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'name' => $this->name,
             'category' => $this->category
         ];
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/Content/V1/ContentModels.php b/src/Twilio/Rest/Content/V1/ContentModels.php
index 43b6862fa..1cbae39e9 100644
--- a/src/Twilio/Rest/Content/V1/ContentModels.php
+++ b/src/Twilio/Rest/Content/V1/ContentModels.php
@@ -315,9 +315,10 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'body' => $this->body
         ];
+        return $jsonString;
     }
 }
 
@@ -341,10 +342,13 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'body' => $this->body,
+        $jsonString = [
             'media' => $this->media
         ];
+        if (isset($this->body)) {
+            $jsonString['body'] = $this->body;
+        }
+        return $jsonString;
     }
 }
 
@@ -377,13 +381,20 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'latitude' => $this->latitude,
-            'longitude' => $this->longitude,
-            'label' => $this->label,
-            'id' => $this->id,
-            'address' => $this->address
+            'longitude' => $this->longitude
         ];
+        if (isset($this->label)) {
+            $jsonString['label'] = $this->label;
+        }
+        if (isset($this->id)) {
+            $jsonString['id'] = $this->id;
+        }
+        if (isset($this->address)) {
+            $jsonString['address'] = $this->address;
+        }
+        return $jsonString;
     }
 }
 
@@ -410,11 +421,14 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'id' => $this->id,
-            'item' => $this->item,
-            'description' => $this->description
+            'item' => $this->item
         ];
+        if (isset($this->description)) {
+            $jsonString['description'] = $this->description;
+        }
+        return $jsonString;
     }
 }
 
@@ -441,11 +455,12 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'body' => $this->body,
             'button' => $this->button,
             'items' => $this->items
         ];
+        return $jsonString;
     }
 }
 
@@ -481,14 +496,23 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'type' => $this->type,
-            'title' => $this->title,
-            'url' => $this->url,
-            'phone' => $this->phone,
-            'code' => $this->code,
-            'id' => $this->id
+            'title' => $this->title
         ];
+        if (isset($this->url)) {
+            $jsonString['url'] = $this->url;
+        }
+        if (isset($this->phone)) {
+            $jsonString['phone'] = $this->phone;
+        }
+        if (isset($this->code)) {
+            $jsonString['code'] = $this->code;
+        }
+        if (isset($this->id)) {
+            $jsonString['id'] = $this->id;
+        }
+        return $jsonString;
     }
 }
 
@@ -512,10 +536,15 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'body' => $this->body,
-            'actions' => $this->actions
+        $jsonString = [
         ];
+        if (isset($this->body)) {
+            $jsonString['body'] = $this->body;
+        }
+        if (isset($this->actions)) {
+            $jsonString['actions'] = $this->actions;
+        }
+        return $jsonString;
     }
 }
 
@@ -542,11 +571,14 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'type' => $this->type,
-            'title' => $this->title,
-            'id' => $this->id
+            'title' => $this->title
         ];
+        if (isset($this->id)) {
+            $jsonString['id'] = $this->id;
+        }
+        return $jsonString;
     }
 }
 
@@ -570,10 +602,11 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'body' => $this->body,
             'actions' => $this->actions
         ];
+        return $jsonString;
     }
 }
 
@@ -609,14 +642,23 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'type' => $this->type,
-            'title' => $this->title,
-            'url' => $this->url,
-            'phone' => $this->phone,
-            'id' => $this->id,
-            'code' => $this->code
+            'title' => $this->title
         ];
+        if (isset($this->url)) {
+            $jsonString['url'] = $this->url;
+        }
+        if (isset($this->phone)) {
+            $jsonString['phone'] = $this->phone;
+        }
+        if (isset($this->id)) {
+            $jsonString['id'] = $this->id;
+        }
+        if (isset($this->code)) {
+            $jsonString['code'] = $this->code;
+        }
+        return $jsonString;
     }
 }
 
@@ -646,12 +688,19 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'title' => $this->title,
-            'subtitle' => $this->subtitle,
-            'media' => $this->media,
-            'actions' => $this->actions
+        $jsonString = [
+            'title' => $this->title
         ];
+        if (isset($this->subtitle)) {
+            $jsonString['subtitle'] = $this->subtitle;
+        }
+        if (isset($this->media)) {
+            $jsonString['media'] = $this->media;
+        }
+        if (isset($this->actions)) {
+            $jsonString['actions'] = $this->actions;
+        }
+        return $jsonString;
     }
 }
 
@@ -687,14 +736,27 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'id' => $this->id,
-            'section_title' => $this->sectionTitle,
-            'name' => $this->name,
-            'media_url' => $this->mediaUrl,
-            'price' => $this->price,
-            'description' => $this->description
+        $jsonString = [
         ];
+        if (isset($this->id)) {
+            $jsonString['id'] = $this->id;
+        }
+        if (isset($this->sectionTitle)) {
+            $jsonString['section_title'] = $this->sectionTitle;
+        }
+        if (isset($this->name)) {
+            $jsonString['name'] = $this->name;
+        }
+        if (isset($this->mediaUrl)) {
+            $jsonString['media_url'] = $this->mediaUrl;
+        }
+        if (isset($this->price)) {
+            $jsonString['price'] = $this->price;
+        }
+        if (isset($this->description)) {
+            $jsonString['description'] = $this->description;
+        }
+        return $jsonString;
     }
 }
 
@@ -730,14 +792,25 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'title' => $this->title,
-            'body' => $this->body,
-            'subtitle' => $this->subtitle,
-            'id' => $this->id,
-            'items' => $this->items,
-            'dynamic_items' => $this->dynamicItems
+        $jsonString = [
+            'body' => $this->body
         ];
+        if (isset($this->title)) {
+            $jsonString['title'] = $this->title;
+        }
+        if (isset($this->subtitle)) {
+            $jsonString['subtitle'] = $this->subtitle;
+        }
+        if (isset($this->id)) {
+            $jsonString['id'] = $this->id;
+        }
+        if (isset($this->items)) {
+            $jsonString['items'] = $this->items;
+        }
+        if (isset($this->dynamicItems)) {
+            $jsonString['dynamic_items'] = $this->dynamicItems;
+        }
+        return $jsonString;
     }
 }
 
@@ -770,13 +843,20 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'type' => $this->type,
-            'title' => $this->title,
-            'url' => $this->url,
-            'phone' => $this->phone,
-            'id' => $this->id
+            'title' => $this->title
         ];
+        if (isset($this->url)) {
+            $jsonString['url'] = $this->url;
+        }
+        if (isset($this->phone)) {
+            $jsonString['phone'] = $this->phone;
+        }
+        if (isset($this->id)) {
+            $jsonString['id'] = $this->id;
+        }
+        return $jsonString;
     }
 }
 
@@ -806,12 +886,21 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'title' => $this->title,
-            'body' => $this->body,
-            'media' => $this->media,
-            'actions' => $this->actions
+        $jsonString = [
         ];
+        if (isset($this->title)) {
+            $jsonString['title'] = $this->title;
+        }
+        if (isset($this->body)) {
+            $jsonString['body'] = $this->body;
+        }
+        if (isset($this->media)) {
+            $jsonString['media'] = $this->media;
+        }
+        if (isset($this->actions)) {
+            $jsonString['actions'] = $this->actions;
+        }
+        return $jsonString;
     }
 }
 
@@ -835,10 +924,11 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'body' => $this->body,
             'cards' => $this->cards
         ];
+        return $jsonString;
     }
 }
 
@@ -862,10 +952,11 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'label' => $this->label,
             'type' => $this->type
         ];
+        return $jsonString;
     }
 }
 
@@ -898,13 +989,20 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'id' => $this->id,
-            'next_page_id' => $this->nextPageId,
-            'title' => $this->title,
-            'subtitle' => $this->subtitle,
             'layout' => $this->layout
         ];
+        if (isset($this->nextPageId)) {
+            $jsonString['next_page_id'] = $this->nextPageId;
+        }
+        if (isset($this->title)) {
+            $jsonString['title'] = $this->title;
+        }
+        if (isset($this->subtitle)) {
+            $jsonString['subtitle'] = $this->subtitle;
+        }
+        return $jsonString;
     }
 }
 
@@ -940,7 +1038,7 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'body' => $this->body,
             'button_text' => $this->buttonText,
             'subtitle' => $this->subtitle,
@@ -948,6 +1046,7 @@ public function jsonSerialize(): array
             'pages' => $this->pages,
             'type' => $this->type
         ];
+        return $jsonString;
     }
 }
 
@@ -974,11 +1073,12 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'id' => $this->id,
             'title' => $this->title,
             'timeSlots' => $this->timeSlots
         ];
+        return $jsonString;
     }
 }
 
@@ -1011,13 +1111,22 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'body' => $this->body,
-            'footer' => $this->footer,
-            'media' => $this->media,
-            'header_text' => $this->headerText,
-            'actions' => $this->actions
+        $jsonString = [
+            'body' => $this->body
         ];
+        if (isset($this->footer)) {
+            $jsonString['footer'] = $this->footer;
+        }
+        if (isset($this->media)) {
+            $jsonString['media'] = $this->media;
+        }
+        if (isset($this->headerText)) {
+            $jsonString['header_text'] = $this->headerText;
+        }
+        if (isset($this->actions)) {
+            $jsonString['actions'] = $this->actions;
+        }
+        return $jsonString;
     }
 }
 
@@ -1041,10 +1150,11 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'type' => $this->type,
             'copy_code_text' => $this->copyCodeText
         ];
+        return $jsonString;
     }
 }
 
@@ -1071,11 +1181,16 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'add_security_recommendation' => $this->addSecurityRecommendation,
-            'code_expiration_minutes' => $this->codeExpirationMinutes,
+        $jsonString = [
             'actions' => $this->actions
         ];
+        if (isset($this->addSecurityRecommendation)) {
+            $jsonString['add_security_recommendation'] = $this->addSecurityRecommendation;
+        }
+        if (isset($this->codeExpirationMinutes)) {
+            $jsonString['code_expiration_minutes'] = $this->codeExpirationMinutes;
+        }
+        return $jsonString;
     }
 }
 
@@ -1132,21 +1247,48 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'twilio/text' => $this->twilioText,
-            'twilio/media' => $this->twilioMedia,
-            'twilio/location' => $this->twilioLocation,
-            'twilio/list-picker' => $this->twilioListPicker,
-            'twilio/call-to-action' => $this->twilioCallToAction,
-            'twilio/quick-reply' => $this->twilioQuickReply,
-            'twilio/card' => $this->twilioCard,
-            'twilio/catalog' => $this->twilioCatalog,
-            'twilio/carousel' => $this->twilioCarousel,
-            'twilio/flows' => $this->twilioFlows,
-            'twilio/schedule' => $this->twilioSchedule,
-            'whatsapp/card' => $this->whatsappCard,
-            'whatsapp/authentication' => $this->whatsappAuthentication
+        $jsonString = [
         ];
+        if (isset($this->twilioText)) {
+            $jsonString['twilio/text'] = $this->twilioText;
+        }
+        if (isset($this->twilioMedia)) {
+            $jsonString['twilio/media'] = $this->twilioMedia;
+        }
+        if (isset($this->twilioLocation)) {
+            $jsonString['twilio/location'] = $this->twilioLocation;
+        }
+        if (isset($this->twilioListPicker)) {
+            $jsonString['twilio/list-picker'] = $this->twilioListPicker;
+        }
+        if (isset($this->twilioCallToAction)) {
+            $jsonString['twilio/call-to-action'] = $this->twilioCallToAction;
+        }
+        if (isset($this->twilioQuickReply)) {
+            $jsonString['twilio/quick-reply'] = $this->twilioQuickReply;
+        }
+        if (isset($this->twilioCard)) {
+            $jsonString['twilio/card'] = $this->twilioCard;
+        }
+        if (isset($this->twilioCatalog)) {
+            $jsonString['twilio/catalog'] = $this->twilioCatalog;
+        }
+        if (isset($this->twilioCarousel)) {
+            $jsonString['twilio/carousel'] = $this->twilioCarousel;
+        }
+        if (isset($this->twilioFlows)) {
+            $jsonString['twilio/flows'] = $this->twilioFlows;
+        }
+        if (isset($this->twilioSchedule)) {
+            $jsonString['twilio/schedule'] = $this->twilioSchedule;
+        }
+        if (isset($this->whatsappCard)) {
+            $jsonString['whatsapp/card'] = $this->whatsappCard;
+        }
+        if (isset($this->whatsappAuthentication)) {
+            $jsonString['whatsapp/authentication'] = $this->whatsappAuthentication;
+        }
+        return $jsonString;
     }
 }
 
@@ -1176,12 +1318,17 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'friendly_name' => $this->friendlyName,
-            'variables' => $this->variables,
+        $jsonString = [
             'language' => $this->language,
             'types' => $this->types
         ];
+        if (isset($this->friendlyName)) {
+            $jsonString['friendly_name'] = $this->friendlyName;
+        }
+        if (isset($this->variables)) {
+            $jsonString['variables'] = $this->variables;
+        }
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/Lookups/V2/BucketModels.php b/src/Twilio/Rest/Lookups/V2/BucketModels.php
index 6363db68e..4e016b2f0 100644
--- a/src/Twilio/Rest/Lookups/V2/BucketModels.php
+++ b/src/Twilio/Rest/Lookups/V2/BucketModels.php
@@ -49,10 +49,15 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'limit' => $this->limit,
-            'ttl' => $this->ttl
+        $jsonString = [
         ];
+        if (isset($this->limit)) {
+            $jsonString['limit'] = $this->limit;
+        }
+        if (isset($this->ttl)) {
+            $jsonString['ttl'] = $this->ttl;
+        }
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/Lookups/V2/LookupOverrideModels.php b/src/Twilio/Rest/Lookups/V2/LookupOverrideModels.php
index 66ac5918c..c7d2af1f2 100644
--- a/src/Twilio/Rest/Lookups/V2/LookupOverrideModels.php
+++ b/src/Twilio/Rest/Lookups/V2/LookupOverrideModels.php
@@ -49,10 +49,15 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'line_type' => $this->lineType,
-            'reason' => $this->reason
+        $jsonString = [
         ];
+        if (isset($this->lineType)) {
+            $jsonString['line_type'] = $this->lineType;
+        }
+        if (isset($this->reason)) {
+            $jsonString['reason'] = $this->reason;
+        }
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/Lookups/V2/QueryModels.php b/src/Twilio/Rest/Lookups/V2/QueryModels.php
index 33ad04486..5f151a32c 100644
--- a/src/Twilio/Rest/Lookups/V2/QueryModels.php
+++ b/src/Twilio/Rest/Lookups/V2/QueryModels.php
@@ -119,18 +119,39 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'first_name' => $this->firstName,
-            'last_name' => $this->lastName,
-            'address_line1' => $this->addressLine1,
-            'address_line2' => $this->addressLine2,
-            'city' => $this->city,
-            'state' => $this->state,
-            'postal_code' => $this->postalCode,
-            'address_country_code' => $this->addressCountryCode,
-            'national_id' => $this->nationalId,
-            'date_of_birth' => $this->dateOfBirth
+        $jsonString = [
         ];
+        if (isset($this->firstName)) {
+            $jsonString['first_name'] = $this->firstName;
+        }
+        if (isset($this->lastName)) {
+            $jsonString['last_name'] = $this->lastName;
+        }
+        if (isset($this->addressLine1)) {
+            $jsonString['address_line1'] = $this->addressLine1;
+        }
+        if (isset($this->addressLine2)) {
+            $jsonString['address_line2'] = $this->addressLine2;
+        }
+        if (isset($this->city)) {
+            $jsonString['city'] = $this->city;
+        }
+        if (isset($this->state)) {
+            $jsonString['state'] = $this->state;
+        }
+        if (isset($this->postalCode)) {
+            $jsonString['postal_code'] = $this->postalCode;
+        }
+        if (isset($this->addressCountryCode)) {
+            $jsonString['address_country_code'] = $this->addressCountryCode;
+        }
+        if (isset($this->nationalId)) {
+            $jsonString['national_id'] = $this->nationalId;
+        }
+        if (isset($this->dateOfBirth)) {
+            $jsonString['date_of_birth'] = $this->dateOfBirth;
+        }
+        return $jsonString;
     }
 }
 
@@ -151,9 +172,12 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'last_verified_date' => $this->lastVerifiedDate
+        $jsonString = [
         ];
+        if (isset($this->lastVerifiedDate)) {
+            $jsonString['last_verified_date'] = $this->lastVerifiedDate;
+        }
+        return $jsonString;
     }
 }
 
@@ -174,9 +198,12 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'partner_sub_id' => $this->partnerSubId
+        $jsonString = [
         ];
+        if (isset($this->partnerSubId)) {
+            $jsonString['partner_sub_id'] = $this->partnerSubId;
+        }
+        return $jsonString;
     }
 }
 
@@ -215,15 +242,28 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'correlation_id' => $this->correlationId,
-            'phone_number' => $this->phoneNumber,
-            'fields' => $this->fields,
-            'country_code' => $this->countryCode,
-            'identity_match' => $this->identityMatch,
-            'reassigned_number' => $this->reassignedNumber,
-            'sms_pumping_risk' => $this->smsPumpingRisk
+        $jsonString = [
+            'phone_number' => $this->phoneNumber
         ];
+        if (isset($this->correlationId)) {
+            $jsonString['correlation_id'] = $this->correlationId;
+        }
+        if (isset($this->fields)) {
+            $jsonString['fields'] = $this->fields;
+        }
+        if (isset($this->countryCode)) {
+            $jsonString['country_code'] = $this->countryCode;
+        }
+        if (isset($this->identityMatch)) {
+            $jsonString['identity_match'] = $this->identityMatch;
+        }
+        if (isset($this->reassignedNumber)) {
+            $jsonString['reassigned_number'] = $this->reassignedNumber;
+        }
+        if (isset($this->smsPumpingRisk)) {
+            $jsonString['sms_pumping_risk'] = $this->smsPumpingRisk;
+        }
+        return $jsonString;
     }
 }
 
@@ -244,9 +284,12 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'phone_numbers' => $this->phoneNumbers
+        $jsonString = [
         ];
+        if (isset($this->phoneNumbers)) {
+            $jsonString['phone_numbers'] = $this->phoneNumbers;
+        }
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/Marketplace/V1/InstalledAddOn/InstalledAddOnUsageModels.php b/src/Twilio/Rest/Marketplace/V1/InstalledAddOn/InstalledAddOnUsageModels.php
index fdb026ad1..ef24e74f4 100644
--- a/src/Twilio/Rest/Marketplace/V1/InstalledAddOn/InstalledAddOnUsageModels.php
+++ b/src/Twilio/Rest/Marketplace/V1/InstalledAddOn/InstalledAddOnUsageModels.php
@@ -62,11 +62,14 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'quantity' => $this->quantity,
-            'sid' => $this->sid,
-            'submitted' => $this->submitted
+            'sid' => $this->sid
         ];
+        if (isset($this->submitted)) {
+            $jsonString['submitted'] = $this->submitted;
+        }
+        return $jsonString;
     }
 }
 
@@ -90,10 +93,13 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'total_submitted' => $this->totalSubmitted,
+        $jsonString = [
             'billable_items' => $this->billableItems
         ];
+        if (isset($this->totalSubmitted)) {
+            $jsonString['total_submitted'] = $this->totalSubmitted;
+        }
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/Marketplace/V1/ReferralConversionModels.php b/src/Twilio/Rest/Marketplace/V1/ReferralConversionModels.php
index cabac010c..6fbc0abf8 100644
--- a/src/Twilio/Rest/Marketplace/V1/ReferralConversionModels.php
+++ b/src/Twilio/Rest/Marketplace/V1/ReferralConversionModels.php
@@ -45,9 +45,12 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'referral_account_sid' => $this->referralAccountSid
+        $jsonString = [
         ];
+        if (isset($this->referralAccountSid)) {
+            $jsonString['referral_account_sid'] = $this->referralAccountSid;
+        }
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/Messaging/V2/ChannelsSenderModels.php b/src/Twilio/Rest/Messaging/V2/ChannelsSenderModels.php
index ba55d047e..78d533678 100644
--- a/src/Twilio/Rest/Messaging/V2/ChannelsSenderModels.php
+++ b/src/Twilio/Rest/Messaging/V2/ChannelsSenderModels.php
@@ -106,12 +106,21 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'waba_id' => $this->wabaId,
-            'verification_method' => $this->verificationMethod,
-            'verification_code' => $this->verificationCode,
-            'voice_application_sid' => $this->voiceApplicationSid
+        $jsonString = [
         ];
+        if (isset($this->wabaId)) {
+            $jsonString['waba_id'] = $this->wabaId;
+        }
+        if (isset($this->verificationMethod)) {
+            $jsonString['verification_method'] = $this->verificationMethod;
+        }
+        if (isset($this->verificationCode)) {
+            $jsonString['verification_code'] = $this->verificationCode;
+        }
+        if (isset($this->voiceApplicationSid)) {
+            $jsonString['voice_application_sid'] = $this->voiceApplicationSid;
+        }
+        return $jsonString;
     }
 }
 
@@ -147,14 +156,27 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'callback_url' => $this->callbackUrl,
-            'callback_method' => $this->callbackMethod,
-            'fallback_url' => $this->fallbackUrl,
-            'fallback_method' => $this->fallbackMethod,
-            'status_callback_url' => $this->statusCallbackUrl,
-            'status_callback_method' => $this->statusCallbackMethod
+        $jsonString = [
         ];
+        if (isset($this->callbackUrl)) {
+            $jsonString['callback_url'] = $this->callbackUrl;
+        }
+        if (isset($this->callbackMethod)) {
+            $jsonString['callback_method'] = $this->callbackMethod;
+        }
+        if (isset($this->fallbackUrl)) {
+            $jsonString['fallback_url'] = $this->fallbackUrl;
+        }
+        if (isset($this->fallbackMethod)) {
+            $jsonString['fallback_method'] = $this->fallbackMethod;
+        }
+        if (isset($this->statusCallbackUrl)) {
+            $jsonString['status_callback_url'] = $this->statusCallbackUrl;
+        }
+        if (isset($this->statusCallbackMethod)) {
+            $jsonString['status_callback_method'] = $this->statusCallbackMethod;
+        }
+        return $jsonString;
     }
 }
 
@@ -196,16 +218,33 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'name' => $this->name,
-            'about' => $this->about,
-            'address' => $this->address,
-            'description' => $this->description,
-            'emails' => $this->emails,
-            'logo_url' => $this->logoUrl,
-            'vertical' => $this->vertical,
-            'websites' => $this->websites
+        $jsonString = [
         ];
+        if (isset($this->name)) {
+            $jsonString['name'] = $this->name;
+        }
+        if (isset($this->about)) {
+            $jsonString['about'] = $this->about;
+        }
+        if (isset($this->address)) {
+            $jsonString['address'] = $this->address;
+        }
+        if (isset($this->description)) {
+            $jsonString['description'] = $this->description;
+        }
+        if (isset($this->emails)) {
+            $jsonString['emails'] = $this->emails;
+        }
+        if (isset($this->logoUrl)) {
+            $jsonString['logo_url'] = $this->logoUrl;
+        }
+        if (isset($this->vertical)) {
+            $jsonString['vertical'] = $this->vertical;
+        }
+        if (isset($this->websites)) {
+            $jsonString['websites'] = $this->websites;
+        }
+        return $jsonString;
     }
 }
 
@@ -235,12 +274,19 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'sender_id' => $this->senderId,
-            'configuration' => $this->configuration,
-            'webhook' => $this->webhook,
-            'profile' => $this->profile
+        $jsonString = [
+            'sender_id' => $this->senderId
         ];
+        if (isset($this->configuration)) {
+            $jsonString['configuration'] = $this->configuration;
+        }
+        if (isset($this->webhook)) {
+            $jsonString['webhook'] = $this->webhook;
+        }
+        if (isset($this->profile)) {
+            $jsonString['profile'] = $this->profile;
+        }
+        return $jsonString;
     }
 }
 
@@ -267,11 +313,18 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'configuration' => $this->configuration,
-            'webhook' => $this->webhook,
-            'profile' => $this->profile
+        $jsonString = [
         ];
+        if (isset($this->configuration)) {
+            $jsonString['configuration'] = $this->configuration;
+        }
+        if (isset($this->webhook)) {
+            $jsonString['webhook'] = $this->webhook;
+        }
+        if (isset($this->profile)) {
+            $jsonString['profile'] = $this->profile;
+        }
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/PreviewIam/Versionless/Organization/RoleAssignmentModels.php b/src/Twilio/Rest/PreviewIam/Versionless/Organization/RoleAssignmentModels.php
index 0e58cdad1..5e89365cb 100644
--- a/src/Twilio/Rest/PreviewIam/Versionless/Organization/RoleAssignmentModels.php
+++ b/src/Twilio/Rest/PreviewIam/Versionless/Organization/RoleAssignmentModels.php
@@ -53,11 +53,12 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
+        $jsonString = [
             'role_sid' => $this->roleSid,
             'scope' => $this->scope,
             'identity' => $this->identity
         ];
+        return $jsonString;
     }
 }
 
diff --git a/src/Twilio/Rest/PreviewIam/Versionless/Organization/UserModels.php b/src/Twilio/Rest/PreviewIam/Versionless/Organization/UserModels.php
index a6b048d9c..aedcc0179 100644
--- a/src/Twilio/Rest/PreviewIam/Versionless/Organization/UserModels.php
+++ b/src/Twilio/Rest/PreviewIam/Versionless/Organization/UserModels.php
@@ -88,10 +88,15 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'givenName' => $this->givenName,
-            'familyName' => $this->familyName
+        $jsonString = [
         ];
+        if (isset($this->givenName)) {
+            $jsonString['givenName'] = $this->givenName;
+        }
+        if (isset($this->familyName)) {
+            $jsonString['familyName'] = $this->familyName;
+        }
+        return $jsonString;
     }
 }
 
@@ -118,11 +123,18 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'primary' => $this->primary,
-            'value' => $this->value,
-            'type' => $this->type
+        $jsonString = [
         ];
+        if (isset($this->primary)) {
+            $jsonString['primary'] = $this->primary;
+        }
+        if (isset($this->value)) {
+            $jsonString['value'] = $this->value;
+        }
+        if (isset($this->type)) {
+            $jsonString['type'] = $this->type;
+        }
+        return $jsonString;
     }
 }
 
@@ -152,12 +164,21 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'resourceType' => $this->resourceType,
-            'created' => $this->created,
-            'lastModified' => $this->lastModified,
-            'version' => $this->version
+        $jsonString = [
         ];
+        if (isset($this->resourceType)) {
+            $jsonString['resourceType'] = $this->resourceType;
+        }
+        if (isset($this->created)) {
+            $jsonString['created'] = $this->created;
+        }
+        if (isset($this->lastModified)) {
+            $jsonString['lastModified'] = $this->lastModified;
+        }
+        if (isset($this->version)) {
+            $jsonString['version'] = $this->version;
+        }
+        return $jsonString;
     }
 }
 
@@ -208,19 +229,40 @@ public function toArray(): array
 
     public function jsonSerialize(): array
     {
-        return [
-            'id' => $this->id,
-            'externalId' => $this->externalId,
-            'userName' => $this->userName,
-            'displayName' => $this->displayName,
-            'name' => $this->name,
-            'emails' => $this->emails,
-            'active' => $this->active,
-            'locale' => $this->locale,
-            'timezone' => $this->timezone,
-            'schemas' => $this->schemas,
-            'meta' => $this->meta
+        $jsonString = [
+            'userName' => $this->userName
         ];
+        if (isset($this->id)) {
+            $jsonString['id'] = $this->id;
+        }
+        if (isset($this->externalId)) {
+            $jsonString['externalId'] = $this->externalId;
+        }
+        if (isset($this->displayName)) {
+            $jsonString['displayName'] = $this->displayName;
+        }
+        if (isset($this->name)) {
+            $jsonString['name'] = $this->name;
+        }
+        if (isset($this->emails)) {
+            $jsonString['emails'] = $this->emails;
+        }
+        if (isset($this->active)) {
+            $jsonString['active'] = $this->active;
+        }
+        if (isset($this->locale)) {
+            $jsonString['locale'] = $this->locale;
+        }
+        if (isset($this->timezone)) {
+            $jsonString['timezone'] = $this->timezone;
+        }
+        if (isset($this->schemas)) {
+            $jsonString['schemas'] = $this->schemas;
+        }
+        if (isset($this->meta)) {
+            $jsonString['meta'] = $this->meta;
+        }
+        return $jsonString;
     }
 }