fix deprecations: use choices_as_values=true and flip content of the choice options

Export/Export/ListActivity.php

@@ -99,6 +99,7 @@ class ListActivity implements ListInterface
             'multiple' => true,
             'expanded' => true,
             'choices' => array_combine($this->fields, $this->fields),
+            'choices_as_values' => true,
             'label'    => 'Fields to include in export',
             'constraints' => [new Callback(array(
                 'callback' => function($selected, ExecutionContextInterface $context) {

Form/ActivityType.php

@@ -102,9 +102,10 @@ class ActivityType extends AbstractType
             ->add('attendee', ChoiceType::class, array(
                'expanded' => true,
                'required' => false,
+               'choices_as_values' => true,
                'choices' => array(
-                  true => 'present',
-                  false => 'not present'
+                  'present' => true,
+                  'not present' => false
                )
             ))
             ->add('user')