param null=True is no working ?

[nonenull]

Example

use a URLField like this :

class Test(Document):
    test = URLField(null=True)

Test.objects.create(test='')

will get a error:

 mongoengine.errors.ValidationError: ValidationError (Test:None) (Invalid scheme  in URL: : ['test'])

[der-joel]

Using null=True will save null in the database if no value (None) was given. To allow empty strings override the URL-Regex (see docs).