check method
      
void
check()
       
    
    
inherited
    Implementation
void check() {
  if (!isInitialized()) {
    final invalidFields = <String>[];
    _fieldSet._appendInvalidFields(invalidFields, '');
    final missingFields = (invalidFields..sort()).join(', ');
    throw StateError('Message missing required fields: $missingFields');
  }
}