/**
  * @param FormBuilderInterface $formBuilder
  *
  * @return string
  */
 protected function getClass(FormBuilderInterface $formBuilder)
 {
     foreach ($formBuilder->getTypes() as $type) {
         if (isset($this->defaultClasses[$type->getName()])) {
             return $this->defaultClasses[$type->getName()];
         }
     }
     return '';
 }