Validation Error on null=true fiels in django

Question

I have created a time filed with arguments Null=True in django model, but it is showing validation error(invalid format) while trying to assign the captured empty value

MY time field is optional as per requirement and have to be captured from front end. It is not allowing empty values code in model walkin_time=models.TimeField(null=True,blank=True)

in view try: newfollowup_lead.walkin_time=request.POST.get('walkin_time', '00:00') except Exception : pass

Error ValidationError at /addfollowupbutton