byContentVal does not update in cases where there are no children

[cuberoot]

Expected Behaviour

A simple model like this should update if the contents of the node changes:

class ButtonModel extends DOMModel {
    @byContentVal() label;
}

Actual Behaviour

The initial contents of the DOM node is read, but the model does not respond to changes

Reproduce Scenario (including but not limited to)

Any use of the byContentVal decorator that isn't in a child node

Steps to Reproduce

I will submit a PR that includes a test case

Platform and Version

Chrome 72, MacOS

Sample Code that illustrates the problem

I will submit a PR that includes a test case

Logs taken while reproducing problem