Set empty_data option to allow empty array to be passed

src/Bundle/ChillMainBundle/Form/WorkflowStepType.php

@@ -150,7 +150,7 @@ class WorkflowStepType extends AbstractType
             ->add('futurePersonSignatures', PickPersonDynamicType::class, [
                 'label' => 'workflow.signature_zone.person signatures',
                 'multiple' => true,
-                'data' => []
+                'empty_data' => '[]',
             ])
             ->add('futureUserSignature', PickUserDynamicType::class, [
                 'label' => 'workflow.signature_zone.user signature',
@@ -159,7 +159,7 @@ class WorkflowStepType extends AbstractType
             ->add('futureDestUsers', PickUserDynamicType::class, [
                 'label' => 'workflow.dest for next steps',
                 'multiple' => true,
-                'data' => [],
+                'empty_data' => '[]',
                 'suggested' => $options['suggested_users'],
             ])
             ->add('futureCcUsers', PickUserDynamicType::class, [
@@ -167,6 +167,7 @@ class WorkflowStepType extends AbstractType
                 'multiple' => true,
                 'required' => false,
                 'suggested' => $options['suggested_users'],
+                'empty_data' => '[]',
                 'attr' => ['class' => 'future-cc-users'],
             ])
             ->add('futureDestEmails', ChillCollectionType::class, [