@leebyron I think I'm struggling to understand how to fix this then. Take this example:

const collection = Immutable.fromJS({a: {b: null}});

// ---------------------------------v [ value is null] 
console.log(collection.getIn(['a', 'b', 'c'], 'notSetValue'); // should return string: 'notSetValue'

As I understand it, the fix for this issue (#1361) is to make it so that when value is falsy or value doesn't have an internal get method BUT that value is null or undefined we want to return the notSetValue. Is that correct?

If so, the only other fix I can think of here is introducing a new conditional, above line 851 that says:

if (value === null || value === undefined) {
  return notSetValue;
}

However, this fix seems to have the same result as the current change in this PR

In Immutable v3, using getIn where an intermediary key in the path was null would return the notSetValue which is what I'm trying to allow here :)

I just put up #1367 which improves the test coverage of getIn and hasIn with tests that would fail for this PR which helps to illustrate my earlier feedback, perhaps you could rebase to include that?

I borrowed your test and tested out a similar change in #1368 - that will both fix this new test while preserving a pass for the rest!