diff --git a/lib/classes/forms/I18n_formattedInput.php b/lib/classes/forms/I18n_formattedInput.php
index 4668a1d232df7b0f021c19247e9af17bde055bdb..d30c5f7c1b6e21963862d71cb32120ad79fb085a 100644
--- a/lib/classes/forms/I18n_formattedInput.php
+++ b/lib/classes/forms/I18n_formattedInput.php
@@ -16,7 +16,11 @@ class I18n_formattedInput extends Input
             $value = $this->value;
         } else {
             $value = [\I18NString::getDefaultLanguage() => $this->value->original()];
-            $value = json_encode(array_merge($value, $this->value->toArray()));
+            $value = array_merge($value, $this->value->toArray());
+            $value = array_map(function ($item) {
+                return $item ?? '';
+            }, $value);
+            $value = json_encode($value);
         }
 
         $template = $GLOBALS['template_factory']->open('forms/i18n_formatted_input');