(mvc) add __empty__ item to OptionField as placeholder for an empty string

src/opnsense/mvc/app/models/OPNsense/Base/FieldTypes/OptionField.php

@@ -59,11 +59,15 @@ class OptionField extends BaseField
             // copy options to internal structure, make sure we don't copy in array structures
             foreach ($data as $key => $value) {
                 if (!is_array($value)) {
+                    if ($key == "__empty__") {
+                        $this->internalOptionList[""] = $value ;
+                    } else {
                         $this->internalOptionList[$key] = $value ;
                     }
                 }
             }
         }
+    }
 
     /**
      * get valid options, descriptions and selected value