isset for formui

/**
 * Magic function __isset returns true or false depending on if the given property is set for this object.
 * Potential valid properties:
 * field: A valid unique name for this control in HTML.
 * value: The value of the control, whether the default or submitted in the form
 *
 * @param string $name The parameter to check
 * @return Boolean Whether the parameter is set
 */
public function __isset($name)
{
  return $this->__get($name) === null;
}