Bug Report:

Whenever the foreign key column of the grid is configured for multi checkbox filtering and is nullable, the value of the "null" option is sent to the server as "NaN".

Steps to replicate:

1. Set ForeignKey column

2. Make the column nullable

3. Set the filterable.multi option to true

4. filter by the null value

A sample project with reproduction has been shared in Ticket with ID: 1463089