FSET if field doesn't exist

Is there a way or appetite to implement an atomic "get then set if not found" operation?

My current use case is that i'm consuming a stream of points and would like to natively keep count of points that match already inserted objects as a field of the matched object. I run multiple clients that connect and work on the same key, and so ideally, i'd like a way to implement a simple locking mechanism via fset/fget. The simplest thing would be if something like the nx operation was usable on fset so that it would ONLY set if the field doesn't exist.