AbstractFileSet.getDirectoryScanner(Project p) throws BuildException("No directory specified for XXXX") even if erroronmissingdir="false" was specified on the fileset. What is the difference between specified dir does not exist and dir was not specified?
The erroronmissingdir="false" setting is used in a situation where you try to create a generic build that may or may not want to include some optional resources - and happily goes on when those optional resources are not there. I'm not sure what a <fileset> without a base directory would be used for, what is your use-case? The only thing I can imagine is something like <zipfileset> which can read from an archive rather than a directory, but this one simply overrides getDirectoryScanner (in ArchiveFileSet).