adding empty data on CFChoice

And fixing a bug occuring because type of empty data are wrong.

fix #23

Form/Type/ChoiceWithOtherType.php

@@ -30,11 +30,13 @@ class ChoiceWithOtherType extends AbstractType
         $options['choices']['_other'] = $this->otherValueLabel;
         //ChoiceWithOther must always be expanded
         $options['expanded'] = true;
+        // adding a default value for choice
+        $options['empty_data'] = null;
         
         $builder
             ->add('_other', 'text', array('required' => false))
             ->add('_choices', 'choice', $options)
-        ;    
+        ; 
     }
 
     /* (non-PHPdoc)
@@ -45,7 +47,9 @@ class ChoiceWithOtherType extends AbstractType
         $resolver
             ->setRequired(array('choices'))
             ->setAllowedTypes(array('choices' => array('array')))
-            ->setDefaults(array('multiple' => false))
+            ->setDefaults(array(
+               'multiple' => false,
+               ))
         ;
     }