[Go] Format error message only when Kind is Struct (#15154)

* Check if Kind is Struct

* Commit regenerated files

* Tabs indentation instead of 4-space

* Commit regenerated files

modules/openapi-generator/src/main/resources/go/client.mustache

@@ -725,16 +725,17 @@ func formatErrorMessage(status string, v interface{}) string {
 	str := ""
 	metaValue := reflect.ValueOf(v).Elem()
 
-	field := metaValue.FieldByName("Title")
-	if field != (reflect.Value{}) {
-		str = fmt.Sprintf("%s", field.Interface())
-	}
+	if metaValue.Kind() == reflect.Struct {
+		field := metaValue.FieldByName("Title")
+		if field != (reflect.Value{}) {
+			str = fmt.Sprintf("%s", field.Interface())
+		}
 
-	field = metaValue.FieldByName("Detail")
-	if field != (reflect.Value{}) {
-		str = fmt.Sprintf("%s (%s)", str, field.Interface())
+		field = metaValue.FieldByName("Detail")
+		if field != (reflect.Value{}) {
+			str = fmt.Sprintf("%s (%s)", str, field.Interface())
+		}
 	}
 
-	// status title (detail)
 	return strings.TrimSpace(fmt.Sprintf("%s %s", status, str))
 }