Allow a box to be created from None

[Dale Stanbrough]

Creating a Box with a parameter of None results in an error.

BoxValueError: First argument must be mapping or iterable

The alternative is

Box(some_value or [])

which works to deliver an empty box.

The Box __init__ method could recognise this situation and create an empty Box instead.

[Chris Griffith]

This is actually done on purpose for safety to mimic how dict operates.

>>> dict(None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not iterable