Issue #3306134: Checkbox fields don't come with proper value for BPMN modellers

modules/modeller_bpmn/src/ModellerBpmnBase.php

@@ -867,7 +867,7 @@ abstract class ModellerBpmnBase extends ModellerBase {
       'label' => $label,
       'weight' => $weight,
       'type' => 'Dropdown',
-      'value' => $value,
+      'value' => $value ? 'yes' : 'no',
       'extras' => [
         'choices' => [
           [