bug: default value on linkedQueryParam

[eneajaho]

Should we always set the defaultValue on linkedQueryParam or only when the change comes from the query params.

Currently:

aParam = linkedQueryParam('a', { defaultValue: 1 });

When a queryParam changes to null or undefined the value of aParam will be set to 1
When we set the value of aParam to null (aParam.set(null)), the value will be null.

The question is: should we always fallback to defaultValue, or only when queryParam changes?