When running the code from this web site:
You will end up with the following problem:
Cause: Error loading class 'mypath.myplugin.Fileset'
The problem seems to be that the <fileset> child of the <configuration> pom.xml element is not translated to the corresponding "FileSet" (upper case S, package of the File Management API) class of Maven File Management API, but maven searches a "Fileset" (lower case S, different package) class in the custom plugin. So it seems the documentation on the web site is not complete, at least the part about "How to tell Maven how to map <fileset> to FileSet class?" is missing.