current property Null safety
The current value of the stream.
When a moveNext call completes with
true, the current field holds
the most recent event of the stream, and it stays like that until the next
call to moveNext. This value must only be read after a call to moveNext
has completed with
true, and only until the moveNext is called again.
If the StreamIterator has not yet been moved to the first element
(moveNext has not been called and completed yet), or if the
StreamIterator has been moved past the last element (moveNext has
false), then current is unspecified. A StreamIterator may
either throw or return an iterator-specific default value in that case.
T get current;