python - Django mptt throwing error when order insertion value is changed -


i have mptt model:

class program_requirement_category(mpttmodel):     display_order = models.integerfield(null=true, blank=true)     name = models.charfield(max_length=100, unique=false)     min_credit = models.integerfield(null=true, blank=true)     max_credit = models.integerfield(null=true, blank=true)     parent = treeforeignkey('self', null=true, blank=true, related_name='children')      class mpttmeta:         order_insertion_by = ['display_order']

when try insert value db, following error:

file "/home/abhishek/projects/mptttree/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1074, in build_filter     raise valueerror("cannot use none query value") valueerror: cannot use none query value

i referred this question , wanted similar work around problem well. how around this?

from mptt documentation:

order_insertion_by list of field names should define ordering when new tree nodes being inserted or existing nodes being reparented, significant ordering field name first. defaults []. it assumed field identified defining ordering never null in database.


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