Fix a bug getting 0

Fix a bug that prevented one to get an attribute of an Item which has 0 value. (Or any value that bool() casts to False.) I'm not quite sure if this change has no side effect.

In the old version when `self.get(name)` returns the value 0.0, `__getattr__` also checked `self.kwargs.get(name)`, which returned None. Where as if I used `.get(name)` directly the expected 0.0 was returned. I think this was also intended in `__getattr__`.