🐛 Bug: Filtering by checkbox columns is inconsistent

[RawmanGrey]

Now, checkboxes can be filtered in UI by using 'is equal' and 'is not equal' with 'false' and 'true' strings.

In REST API docs, 'is' and 'isnot' comparison operators exist for boolean values, - but only 'isnot, null' query works.

However, query results can be filtered by checkboxes with 'eq' operator. Weird enough, 'not' operator has no effect on 'true' and 'false' strings.

I think, solution should be:

• Add new comparison options in filter UI to be used with checkboxes, which have to treat 'null' values as false ones.
• Fix 'is' and 'isnot' to work as declared in docs.

---

Node: v12.22.12
Arch: x64
Platform: linux
Docker: true
Database: pg
ProjectOnRootDB: true
RootDB: pg
PackageVersion: 0.90.11

[RawmanGrey]

As mentioned in #2001 it's problematic to get null values. However there is a sick workaround:

1. create formula field with CONCAT(target_column_with_null_values, "postfix")
2. filter values equal to 'postfix', e.g. where=(target_column_with_null_values,eq,postfix)