I can't believe this !!

[MesmerizedInTheMorning via Digitalmars-d-learn]

https://issues.dlang.org/show_bug.cgi?id=15331

but it's true !

There's **nothing** to check the availability of a Key. At least 
I would expect opIndex[string key] to return a JSONValue with 
.type == JSON_TYPE.NULL, but no...

Also If it was returning a JSONValue* it would be easyer to check 
if a key is present.

God damn it, how could you miss this design flaw when std.json 
was reviewed ?!