Null not correctly reprsented in JSON output

[dfmorrison]

If, in nodeGame, I do

node.game.memory.add({player: node.player.id, stage: node.player.stage, data: { "foo": null }});
node.game.memory.save("data.json");

I get

​{
"player": "681934395222262",
"stage": {
"stage": 2,
"step": 1,
"round": 1
},
"data": {
"foo": "!?_null"
},
"timestamp": 1516569132070
}​

where instead I would have expected something like

​{
"player": "681934395222262",
"stage": {
"stage": 2,
"step": 1,
"round": 1
},
"data": {
"foo": null
},
"timestamp": 1516569132070
}​