Attempting to cast a JSON to a string fails with columnar back end

After upgrading to Knime 5.1 and turning on the columnar back end for a workflow I get the following error when attempting to cast a Json to string in a string manipulation node. I’m using “string($roots$)” where $roots$ is the Json column. Also attempted to use “join($roots$)” which worked on my Mac but still fails in the same way when running the workflow in our other Ubuntu environment.

Changing back to the row based back end removes the error, but I’m trying to run this workflow with the columnar back end due to some memory issues.

ERROR KNIME-Worker-49-String Manipulation 3:1368:1158 Node Execute failed: class org.knime.core.data.json.JSONCell cannot be cast to class java.lang.Integer (org.knime.core.data.json.JSONCell is in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @11025004; java.lang.Integer is in module java.base of loader ‘bootstrap’)

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