What happened

After upgrading from 3.x to 4.x the getIn() method is not behaving as before and not as documented. It often returns Invalid keyPath: Value at ["someKey"] does not have a .get() method: null instead of handling null keys gracefully.

How to reproduce

const ABRecord = Immutable.Record({ a: 1})
const myRecord = new ABRecord()
console.log(myRecord.getIn(['a', 'b']));

Returns

TypeError: Invalid keyPath: Value at ["a"] does not have a .get() method: 1

But I expected it to return null instead.