Using empty() on dynamic fields raises RQLFilterValueError: RQL Value error.

[Brandon]

When a filter is specified like the example, then json_data.key=empty() raises RQLFilterValueError. =null() works accordingly.

{
    'filter': 'json_data.key',
    'source': 'json_data__key',
    'dynamic': True,
    'field': CharField(null=True),
},

[Brandon]

I fixed this error. The CharField should be CharField(null=True, blank=True). It would be helpful to have raise more helpful messages.

django-rql/dj_rql/filter_cls.py

Line 950 in 00f5703

 raise ValueError 

[Max Kolyubyakin]

@ZipBrandon thx for feedback, we will consider!