Proposal: allow to map atoms to other values to handle null -> nil

[Overbryd]

This is the best I could come up with, to handle JSON encoding for projects building upon a different world view (e.g. erlang dependencies classifying nil as null atoms).

Related to that is this question posted on Stackoverflow: https://stackoverflow.com/questions/47895651/how-to-extend-an-existing-protocol-in-elixir/47901896

Outline

As a user of a JSON encoding library, I want to be able to specify atoms to be mapped differently at will to incorporate custom encodings depending on the applications/dependencies needs.

This solves a problem I was having encoding JSON with input coming from an erlang library using :null to encode what should be nil in our world.

Funny side note: "Null References The Billion Dollar Mistake"