Internal Link field: when "None" is selected the value should be null

[giseleblair]

When an "internal link" field type is configured to a model, the initial value of this field is null. When a user selects None from the dropdown in the UI, this value is then returned as "0" as opposed to null

If a user selects None then the value returned should be null to keep the consistency of when a user selects or does not select a value from this field type.

Also note in the screenshot, that when a user does explicitly select None from the dropdown, then the dropdown will display an item that says Selected item not found: 0