Permit null for identity & label arguments.
Permit null for identity & label arguments.

We currently require these values, if specified, to be undefined
or an object/string; we should accept null as well.

apaprocki/blpapi-node,bloomberg/blpapi-node,apaprocki/blpapi-node,bloomberg/blpapi-node,jmptrader/blpapi-node,bloomberg/blpapi-node,apaprocki/blpapi-node,jmptrader/blpapi-node,jmptrader/blpapi-node