Automation trace fails when using automation script in an automation chain

If a workflow transition calls an automation chain which includes an automation script, and automation tracing is enabled, a UnsupportedOperationException is thrown when generating the trace.

To reproduce the problem, install 7.10 with HF04 and deploy the attached Studio jar. Make a file document and start the Simple workflow on it, then Approve the document. In TracePrinter.java at line 177 the documents context variable is being appended to the string builder, but this fails because it is a DocumentWrapper where normally it would be a DocumentModelImpl or DocumentModelListImpl, and DocumentWrapper has no way to convert to a string.