fix(dropdown): handle empty default value to prevent error

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
 - Fix migration error caused by unknown itemtype in containers
+- Fix empty default value in multiple dropdown fields
 
 ## [1.23.2] - 2025-12-22
 

inc/container.class.php

@@ -1369,7 +1369,9 @@ public function updateFieldsValues($data, $itemtype, $massiveaction = false)
                     $data[$field_name] = json_encode(array_values(array_unique(array_merge($existing_values, $new_values))));
 
                 } else {
-                    $data[$field_name] = json_encode($data[$field_name]);
+                    $value = $data[$field_name];
+                    $value = is_array($value) ? $value : [];
+                    $data[$field_name] = json_encode($value);
                 }
             } elseif (array_key_exists('_' . $field_name . '_defined', $data)) {
                 $data[$field_name] = json_encode([]);

inc/field.class.php

@@ -1276,7 +1276,8 @@ public static function prepareHtmlFields(
                 // - either from a previous input (it will be an array).
                 //
                 // -> Decode it only if it is not already an array.
-                $value = json_decode((string) $value);
+                $decoded = json_decode((string) $value, true);
+                $value = is_array($decoded) ? $decoded : [];
             }
 
             $field['value'] = $value;