[Filter plugin] Fields with "Checkboxes set" type do NOT work

When I build a filter box with fields in which its type is "checkboxes set", the field won't work in frontend.

Precondition: at least one listing was posted with the listing field
Steps:
- Create a listing field with type of "checkboxes set"
- Build a listing form containing the listing field above
- Install and activate Filter plugin
- Build a Filter Box with the listing field above
- Go to the page that the Filter Box being visible in frontend
- Select one of checkboxes belonging to the listing field and click Apply

Actual result: the listing is not displayed after apply filter.
Expected result: the listing should display after apply filter.

Please include the bug fix in the next update because this is a premium plugin and a major functionality.