Make array and map types optional by default

[mweststrate]

No description provided.

[mweststrate]

array and map types will be optional by default when used directly as model properties.

Tried making child objects optional as well, but this became very confusing in combination with maybe and such (since undefined would then be an acceptable value, leaving a field in a snapshot would be inferred to {} instead of null, etc..

[mweststrate]

Scheduled for 3.0, closing

[jlgrall]

How to make them mandatory when I need it ?

Seems to me the only way would be adding a refinement() over the current implicit optional() wrapping:

var MyList = types.model({
	list: types.refinement(types.array, v => v !== undefined);
});

Would this refined type still return true with a call to isOptionalType(value) ?