500 After Post to Facet Counts Endpoint

[ephes]

Posting to the facet counts endpoint leads to an internal server error:

                self.validate_constraints(exclude=exclude)
            except ValidationError as e:
                errors = e.update_error_dict(errors)
        if errors:
            raise ValidationError(errors)
    def clean_fields(self, exclude=None):
        """
        Clean all fields and raise a ValidationError containing a dict
        of all validation errors if any occur.