Source: ypserv Version: 4.2-3 Severity: serious rpc.yppasswdd/yppasswd.x is not documented in d/copyright. Please note that it has a non-free license but was relicensed under a BSD license. Your Build-Depends libnsl-dev has the relicensed version that you can use for the build after repacking your source code.
It would also be possible to document in d/copyright that you use this file under the new license.
