taverna-engine has a static method org.apache.taverna.platform.execution.impl.local.T2ReferenceConverter.convertPathToObject() which converts a DataBundle Path to a classical List<String> or equivalent.
It turns out that the Workbench also tries to use this method, but can't as it is hidden inside .impl.
Thus my suggestion is to promote this method to DataBundles.resolve().
I think also the method could be improved to resolve byte and other types than String, to avoid massive memory consumption.
Perhaps also a typed .resolveAsStream() could be useful, e.g. resolveAsStream(outputs, ErrorDocument.class) would find all the errors (in any order).