Github user bowenli86 commented on the issue:
https://github.com/apache/flink/pull/5356
I also agree that changing `get()` API may not be good because it will
break user's logic.
From a user point of view, I found that receiving `null` from `get()` API
is a bit inelegant and confusing. As a user, instinctively, I'd expect an empty
Iterable when there's no state value. In practice, I had to debug several times
and ended up finding the true semantics of `get()`. This is where
`iterator()`'s value lies - to help users avoid such cases.
Frankly, the `iterator()` API is not hard to maintain at all. It only
invokes `get()`, handles the `null` situation, and returns users an empty
iterable.
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