mongoengine unset function inside update operation did not handle default attributes of model object.

# MODEL PROPERTY
status = StringField(default="A") # A, B, C

# UNSET FUNCTION 
model_class.update(unset__status=1)
:- This operation delete status from given model

# MODIFY
model_class.status = 'C'
model_class.save()
:- This function did not create status row in database.