Filtering to a range of integers with a row filter

This should be a ridiculously simple operation and I can’t figure out why it doesn’t work. I have a table with an integer column that I need to filter to a range of integers specified by two flow variables “start” and “end.” Console is showing this error: “Errors loading flow variables into node : Coding issue: Cannot invoke “String.getBytes(java.nio.charset.Charset)” because “” is null”

I created a very simple workflow with only the two columns that I then convert to integer flow variables with the Table Row to Variable node and feed them into the Row Filter node:

Not sure where to go from here. Do I need to do something with org.knime…IntCell ?