public function getHelper($helperType)
    {
        if ($this->isValidKey($helperType)) {
            return $this->getHelperMap()->get($helperType);
        } else {
            throw new InvalidArgumentException('Invalid form helper type given');
        }
    }
public function getHelper($helperType)
    {
        if ($this->isValidKey($helperType)) {
            return $this->getHelperMap()->get($helperType);
        } else {
            throw new InvalidArgumentException('Invalid form helper type given');
        }
    }
public function getHelper ( $ helperType ) { if ( $ this -> isValidKey ( $ helperType ) ) { return $ this -> getHelperMap ( ) -> get ( $ helperType ) ; } else { throw new InvalidArgumentException ( 'Invalid form helper type given' ) ; } }
return registered form helper

@param       string      $helperType         helper type eg. tag, option, field, choise
@return      Map

@throws InvalidArgumentException
return registered form helper