The amazon support module in the enterprise cluster includes a file empty.war. This file contains a web.xml and a sample jsp file.
The file was build as part of the build process and was accidentally checked in.
As the file contained in the file are included in the runtime distribution, the war file can be created on the fly and thus does not need to be included in source or binary form.
As this is against the ASF policy, this is marked as priority blocker.