Handle empty array_agg in I18nInput.FillArray

array_agg returns [null] instead of [] when it can not find any rows,
thus the range enters the loop, but it fails to convert the null to
string.

pkg/form/input.go

@@ -76,7 +76,11 @@ func (input I18nInput) FillValue(r *http.Request) {
 
 func (input I18nInput) FillArray(array database.RecordArray) error {
 	for _, el := range array.Elements {
-		tag, err := language.Parse(el.Fields[0].Get().(string))
+		lang := el.Fields[0].Get()
+		if lang == nil {
+			continue
+		}
+		tag, err := language.Parse(lang.(string))
 		if err != nil {
 			return err
 		}