function hasError($id = null)
 {
     return $id && $this->error && $this->error->is($id) || !!$this->error;
 }
 function setError(FormControlError $error)
 {
     Assert::isFalse($error->is(FormControlError::MISSING), '%s cannot be missing', get_class($this));
     return parent::setError($error);
 }