use _build_filters function instead of specifying request params manuall...

...y
Hm, with this approach, value attribute key will be set to `Filter.1.Value.1`, previously it was set to `Filter.1.Value`.

Are you sure this will still work? We could modify `_build_filters` to remove `.1` suffix if filter has only one value, but might break an existing code and needs to be tested.