Minor Description
TINKERPOP-2605 changed null semantics to allow null as an argument in more places so that has(null) should not throw a NPE any more and instead filter all traversers out.
HasContainer however still throws a NPE if the key is null.
I discovered this when trying to update JanusGraph as that folds in a HasContainer like this which leads to the NPE and thus failing tests.
The same behavior can also be produced with just TinkerGraph and for example the following traversals:
g.V().has(null, 1) g.V().has(null, P.neq(null))