_AuthTokenProvider.onTokenChanged' ('Stream<String?> Function()') isn't a valid override of 'AuthTokenProvider.onTokenChanged

[sgehrman]

Code has errors

[{ "resource": "/home/steve/Documents/GitHub/forks/firebase_admin/lib/src/database.dart", "owner": "generated_diagnostic_collection_name#0", "code": { "value": "invalid_override", "target": { "$mid": 1, "external": "https://dart.dev/diagnostics/invalid_override", "path": "/diagnostics/invalid_override", "scheme": "https", "authority": "dart.dev" } }, "severity": 8, "message": "'_AuthTokenProvider.onTokenChanged' ('Stream<String?> Function()') isn't a valid override of 'AuthTokenProvider.onTokenChanged' ('Stream<Future<String>?> Function()').", "source": "dart", "startLineNumber": 25, "startColumn": 23, "endLineNumber": 25, "endColumn": 37 }]