The None, True, and False values are singletons.
All variable *comparisons* to singletons should use 'is' or 'is not'.
All variable *evaluations* to boolean should use 'if' or 'if not'.
All Object type comparisons should use isinstance()
instead of comparing types directly.
Change-Id: I47863c4862791022670619f19b8bc15d8a93fd81
8b09723a00