What do with nodes that does not produce output in loops?

I have a loop with two "Chemistry External tool"-nodes. I wary the parameters for the first node using flow variables and sometimes this node will not produce any output and give a "Output 1 has no data in output port" error message. This does not seem to be a problem as the flow continues anyway.

But when I feed the output data from the first node into the second node this node can not run and I get an "Execute failed: Output files not found."-error which stops the loop.

Is there some generic way to solve problems like this?



With KNIME 2.3, we have released the so-called workflow switches (category: Flow Control >> Switches). Those allow disabling certain branches of the workflow depending on predefined and parameterizable criteria. I think, this should help to solve your problem...

Regards, Thomas