NULL and non-existent values could be returned from a Tag's query when an XML/JSON node does not exist or when the node does not contain data.

Previously in Windward, NULL and non-existent values when they were returned in these cases to Set, Query, and Switch Tags caused the Tag variable to become invalid in the template; any Tag using that variable would no longer find the template variable when executing. 

In version 16.3.0 this functionality is changed so that the template variable remains in the template and the value is set to a non-value. This allows Tags in the template referencing the variable to be evaluated instead of throwing errors.