[Bug Fix]: Handle null property types in OpenAPI 3.1.0 schemas - DefaultCodegen.java

[Prsolver]

Fixed #12666

Description

This PR fixes an issue where string, boolean, and integer properties were being incorrectly converted to Object types when generating code from OpenAPI 3.1.0 specifications. The root cause was that the swagger-parser may return properties with null types when parsing OpenAPI 3.1.0 schemas (which use JSON Schema 2020-12), causing the getSwaggerType() method to return null, which then propagated through to the generated code as Object.

Changes:

• Modified getSwaggerType() in DefaultCodegen.java to handle null property types gracefully
• Added inferTypeFromFormat() helper method to infer types from format strings when type is null (e.g., int32 → integer, date-time → DateTime)
• Added final fallback to return "object" instead of null, preventing the "String to be sanitized is null. Default to Object" error
• Added comprehensive test cases to verify the fix works correctly for various scenarios
• Preserved all existing functionality
• Maintained backward compatibility - the public API is unchanged

Contribution by Gittensor, see my contribution statistics at https://gittensor.io/miners/details?githubId=100145226

[Prsolver]

Hi, @djankows

This is ready for review, thanks