Suggestion: allow definition of final selector for component use

[jmbldwn]

Currently the selector returns null to indicate data needs to be acquired.

But a component usually doesn't care. If the data is an array, it would be best if the selector returned [] instead of null, so components don't need to null-check.

This could be a way of indicating the type of the result (array, object, number, string....) that would present an empty value for each one ([]. {}. NaN, ''), or a function supplied to the constructor that specifies the null check applied to the selector before output.