python - django user creation form required keyerror -

i made custom registration form, inherits usercreationform. however, when try submit, 1 of fields empty, keyerror on required. seems happen somewhere in django source code, i'm pretty sure comes because of custom clean method.

form:

class registrationform(usercreationform):     """     edit user registration form add emailfield     """      class meta:         model = user         fields = ('username', 'password1', 'password2')      def __init__(self, *args, **kwargs):         super(registrationform, self).__init__(*args, **kwargs)         #add custom errormessages         self.fields['username'].error_messages = {         'invalid': 'invalid username'         }         self.fields['password2'].label = "confirm password"      #make sure username lowered , unique     def clean_username(self):         username = self.cleaned_data.get('username')         try:             user.objects.get(username__iexact=username)             raise forms.validationerror("this username in use.")         except user.doesnotexist:             pass          return username      def save(self, commit=true):         user = super(registrationform, self).save(commit=false)         if commit:             user.save()         return user 

the errorlog http://pastebin.com/8y6tp7rw

note: using django 1.8

you replacing of 'username' field error_messages dict own dict. instead, should update error_messages dict custom message so:

self.fields['username'].error_messages.update({     'invalid': 'invalid username' })