CiviCRM_API3_Exception: array_key_exists() - all working with 5.40

Further inspection of the Automated test output that identified this regression: financial#180 (closed)

Identifies another issue with dev-master: CiviCRM_API3_Exception: array_key_exists(): The first argument should be either a string or an integer

This test passed with 5.40 ✅ but fails ❌ with dev-master (and possibly RC)