Fix incorrect NULL values in TABLE_CATALOG returned by getSchemas() for built-in schemas.

[Ananya2]

Summary

Fix incorrect NULL values in TABLE_CATALOG returned by getSchemas() for built-in schemas.

Problem

DatabaseMetaData.getSchemas() was returning NULL for the TABLE_CATALOG column when querying built-in schemas such as dbo, guest, sys, INFORMATION_SCHEMA, and database roles.
According to the JDBC specification, TABLE_CATALOG should contain the name of the catalog (database) in which the schema resides and should only be NULL when the value is not applicable.

Root Cause

The issue originated from the query logic backing getSchemas(). The implementation contained a CASE statement that explicitly set TABLE_CATALOG to NULL for schemas included in an internal constSchemas list representing built-in schemas. While intended to special-case system schemas, this logic unintentionally suppressed valid catalog values. As a result, built-in schemas were returned as null.

Solution

The fix removes the special CASE handling entirely and simplifies the catalog derivation logic. Instead of conditionally nulling the catalog name, the method now always resolves the correct catalog based on the input parameters:

• when no catalog is specified, the current database name is returned (DB_NAME())
• when a catalog is provided, that value is returned
• when an empty catalog string is supplied, the catalog is treated as not applicable and NULL is returned for cross-database scenarios

With this change, built-in schemas are treated consistently with user schemas, and the driver now accurately reflects catalog ownership as required by the JDBC specification.

Closes #2863

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.06%. Comparing base (0eb40a0) to head (efc38f6).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2872      +/-   ##
============================================
+ Coverage     59.01%   59.06%   +0.05%     
- Complexity     4751     4753       +2     
============================================
  Files           151      151              
  Lines         34564    34575      +11     
  Branches       5769     5776       +7     
============================================
+ Hits          20399    20423      +24     
+ Misses        11406    11403       -3     
+ Partials       2759     2749      -10     

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