title: peewee IntegrityError: NOT NULL constraint failed: terms.sets_id
body: <p>I have the below model and getting a <code>IntegrityError: NOT NULL constraint failed: terms.sets_id</code> error. I've checked other posts and the only thing I can find that should be causing it is that I'm not passing in all the parameters, but I declare five fields, and pass in 5 values into <code>concept = cls(...)</code>. What am I missing?</p>
  
  <pre><code>class Terms(UserMixin, BaseModel):
      term_id = CharField()
      sets_id = CharField()
      term_count = IntegerField()
      term = TextField()
      definition = TextField()
  
      @classmethod
      def include_term(cls, set_id, term_id, definition, rank, term, **kwards):
          try:
              cls.select().where(cls.term_id == term_id).get()
          except cls.DoesNotExist:
              print("putting term into db")
              concept = cls(
                  set_id = set_id,
                  term_id = term_id,
                  term= term,
                  definition = definition,
                  rank = rank )
              concept.save()
              print(concept.term)
              print("term saved to db")
              return concept
          else:
              raise Exception("Term with that id already exists")
  </code></pre>