To really get this clear, here's my for-beginners answer:
You inputed the arguments in the wrong order.
A keyword argument has this style:
nullable=True, unique=False
A fixed parameter should be defined: True, False, etc. A non-keyword argument is different:
name="Ricardo", fruit="chontaduro"
This syntax error asks you to first put name="Ricardo"
and all of its kind (non-keyword) before those like nullable=True.