fix(recency): handle empty tables returning NULL

[dinaatmiro]

Problem

When a table is completely empty, the recency test incorrectly passes instead of failing.

Root Cause

When a table has no data, MAX(field) returns NULL. The current WHERE clause:

where most_recent < {{ threshold }}

With most_recent = NULL, the comparison NULL < threshold evaluates to NULL (not TRUE), so the WHERE clause filters out the row and returns zero rows — causing the test to pass.

Reproduction

1. Create an empty table
2. Add a recency test to it
3. Run dbt test — the test passes even though there's no recent data

Solution

Add OR most_recent IS NULL to the WHERE clause:

where most_recent < {{ threshold }}
   or most_recent is null

This ensures the test fails when:

• The table has data older than the threshold (most_recent < threshold)
• The table is completely empty (most_recent IS NULL)

Testing

Verified locally with an empty Snowflake table that was previously passing the recency test incorrectly.