Typings for find don't include undefined

[cartant]

Bug Report

Current Behavior

The overload signatures for find don't reflect the operator's behaviour.

The return types are OperatorFunction<T, S> and MonoTypeOperatorFunction<T>.

However, the operator will emit undefined if no match is found. See this test.

Possible Solution

The return types should be OperatorFunction<T, S | undefined> and OperatorFunction<T, T | undefined>.