create advanced_filter_controller

core/lib/utils/string_convert.dart

@@ -0,0 +1,10 @@
+class StringConvert {
+ static String? writeEmptyToNull(String text) {
+    if (text.isEmpty) return null;
+    return text;
+  }
+
+ static String writeNullToEmpty(String? text) {
+    return text ?? '';
+  }
+}