Error creating geometry from value 'null' (String input unrecognized as WKT EWKT, and HEXEWKB.)

[Vayel]

Hi!

Thanks for this package! When used with https://github.com/makinacorpus/django-leaflet and no initial value, GeoJSONFormField raises the follow error:

Error creating geometry from value 'null' (String input unrecognized as WKT EWKT, and HEXEWKB.)

Indeed, the value is None and is dumped by JSONField into "null". The initial value should be jsonfield.forms.InvalidJSONInput(""). It can be set here if undefined: https://github.com/makinacorpus/django-geojson/blob/master/djgeojson/fields.py#L51

[Vayel]

Can be set for model fields as well.

[Vayel]

Actually, it should be set for model fields as well because a field with blank=True will raise the error above.

Can be done with https://docs.djangoproject.com/en/4.0/howto/custom-model-fields/#converting-values-to-python-objects

[dchaplinsky]

Actually, this change is causing a different error.

When using such field in the inlines, with blank=True, django will think that form is changed even if it is not, because it compares "" with InvalidJSONInput('') and marks the form of the formset as one that needs to be saved.

I fixed it with geo = PointField(_("Geo"), blank=True, default=lambda: InvalidJSONInput('')), but I think the proper fix is to overload _has_changed method of the base field class.