Hi @sherknime ,
As you have discovered, there isn’t a place to anchor the flow variable when the table is empty.
This is an example use case for the “NodePit Power nodes”(formerly the “NoOp” / “No operation” ) nodes.
You don’t need those nodes, but they do make life simple and their purpose is clearer. The alternative is is place any node that does nothing (or even does something that you can safely ignore) and then use the flow port from that node.
e.g. before installing “NoOp”, I regularly used Add Empty Rows in this scenario (and had my own component that wrapped it!).
Just configure it to Add “an additional” zero rows! 
e.g. Here is what the flow could look like using the alternative options:
Details below re Nodepit Powernodes, with thanks to @danielesser
Make sure you configure nodepit for your version of KNIME using the drop down on top right of the nodepit page
