xlog can not work will for can not write log into file

There is a big bug in xlog module,reporting 'path' no define when I try to write log into a file.
Anyone find this bug or how to config the log define?
I have configed the log define by the doc,but the issue is still exist.

Start with the xlog module and its documented file-logging configuration, reproducing the reported “path” not defined error. Trace where the configured path is read and compare that behavior with the documentation; the issue is done when the documented configuration writes logs to a file without the error.

Written by the indexing model from the issue text.