[keshavdandeva]

b/577456210

Summary

Fixes a NullPointerException when calling getMetaData() or findColumn() on 0-row ResultSet instances returned by BigQueryDatabaseMetaData when empty ("") or null filter arguments trigger early-exit guards.

Changes

• Added BigQueryJsonResultSet(Schema schema) constructor to initialize 0-row result sets with a non-null Schema.
• Updated all 11 early-exit guards in BigQueryDatabaseMetaData (getTables, getColumns, getSchemas, getProcedures, getProcedureColumns, getFunctions, getFunctionColumns, getPrimaryKeys, getImportedKeys, getExportedKeys, getCrossReference) to pass their respective Schema when returning an empty BigQueryJsonResultSet.
• Simplified the remaining 10 unsupported-feature metadata methods and the PCNT early return in getExportedKeys to use new BigQueryJsonResultSet(schema) instead of allocating single-element LinkedBlockingQueue instances.
• Added parameterized unit tests in BigQueryDatabaseMetaDataTest verifying ResultSetMetaData column counts, column names, and findColumn() across all early-exit paths.

[gemini-code-assist]

Code Review

This pull request updates several metadata methods in BigQueryDatabaseMetaData to return an empty BigQueryJsonResultSet initialized with the correct schema when early-returning due to empty or null arguments, or when the feature is unsupported. A new constructor was added to BigQueryJsonResultSet to support this, and a parameterized test was introduced to verify the behavior. The reviewer pointed out that the @MethodSource factory method emptyArgumentMetadataProvider() in the new tests must be static in JUnit 5 to prevent test execution failures, and provided a refactoring suggestion to resolve this.