Prevent ArrayNode's tryFind from returning Some null when looking for a non-existent key.
Prevent ArrayNode's tryFind from returning Some null when looking for a non-existent key.

basarat/FSharpx.Collections,YaccConstructor/FSharpx.Collections,fsprojects/FSharpx.Collections,fsprojects/FSharpx.Collections,xavierzwirtz/FSharpx.Collections,yever/FSharpx.Collections,gsvgit/FSharpx.Collections