Our current APIVersion object has an is_null method to check when the
version instance is null (major=0 and minor=0).
While this works it is not very pythonic, since you have to write
expressions such as:
if not min_version and not max_version:
return True
elif ((min_version and max_version) and
max_version.is_null() and min_version.is_null()):
return True
This patch removes the is_null method and instead implements the truth
value testing to simplify expressions and make code more pythonic.
So previous code would just look like:
if not min_version and not max_version:
return True
Because this will work with min_version being None or being an
APIVersion instance with major=0 and minor=0.
Change-Id: I7497c5dc940c1e726507117cadbad232d8c1d80d
8b5a772e36