Fixed issue with multiple values in a custom field and AbstractGetSingleAction.

CHANGELOG.md

@@ -3,6 +3,7 @@ Version 1.42 (not yet released)
 
 * Escaping configuration values of custom fields and custom groups. In case a @ or % sign is present in the help or description text
   of the custom field or custom group.
+* Fixed issue with multiple values in a custom field and AbstractGetSingleAction.
 
 Version 1.41
 ------------

Civi/ActionProvider/Action/AbstractGetSingleAction.php

@@ -116,7 +116,13 @@ abstract class AbstractGetSingleAction extends AbstractAction {
       if (substr($custom_id, -3) === '_id') {
         $custom_id = substr($custom_id, 0, -3);
         unset($entity[$field]);
-        $entity['custom_'.$custom_id] = $value;
+        if (is_array($value)) {
+          $entity['custom_' . $custom_id] = array_keys($value);
+        } else {
+          $entity['custom_' . $custom_id] = $value;
+        }
+      } elseif (is_numeric($custom_id) && is_array($value)) {
+        $entity['custom_' . $custom_id] = array_keys($value);
       }
     }
     return $entity;