Removed null check for result array

[netsgnut]

This PR proposes removing a null check from the exec callback.

Currently when the filled values are not truthy (e.g. null or 0), it will not be filled into the virtual field, even when the default value is specified. There are cases where filling in a falsy value is part of the expected behavior, though.

Please advise if this is the correct approach to this. Thanks.

[wclr]

Can you add test for this case?

[netsgnut]

Thanks for the comment. After reading a bit more on the code, I think I might need a clarification as well, as it seems the problem that I had may stem from a misunderstanding.

The code that I tried to make it work is something as:

userSchema.fill('existentialCrisis').multi(function (users, ids, callback) {
  callback(null, ids.map(_id => null))
})

However it seems to work in some cases:

userSchema.fill('existentialCrisis').multi(function (users, ids, callback) {
  callback(null, ids.map(_id => ({ _id, existentialCrisis: null )))
})

I am not sure if the first code snippet (use of fill with multi only and ability to return falsey values) is a canonical use case that we should support, though.

[netsgnut]

It seems I cannot reliably isolate a test case here. Let's close it for now? Thanks.