Using `Object.create(null)` instead of `{}`

[thefourtheye]

We use for..in or if..in more often in other functions, which will give us unexpected results with inherited properties from the prototype chain. So, its safer to use Object.create(null)

[kriskowal]

Note that Dict "mangles" the keys that are added to the internal dictionary store, so there is no chance of a collision with Object.prototype or __proto__. Object.create is unnecessary and limits backward-compatibility (though this is certainly not the longest pole in that tent).