adding formatter for list in spreadsheet (ods, xlsx)

Form/Type/Export/PickFormatterType.php

@@ -56,7 +56,8 @@ class PickFormatterType extends AbstractType
         $builder->add('alias', ChoiceType::class, array(
             'choices' => $choices,
             'choices_as_values' => true,
-            'multiple' => false
+            'multiple' => false,
+            'placeholder' => 'Choose a format'
         ));
 
         //$builder->get('type')->addModelTransformer($transformer);