[monitoring-plugin-perl] Merge pull request #5 from daku3649/patch-1

[Sven Nierlein]

 Module: monitoring-plugin-perl
 Branch: master
 Commit: 049e72d923cf9b68c1c1adc9db5d7c4d4fc3d49e
 Author: Sven Nierlein <sven at nierlein.org>
   Date: Thu Dec  3 12:37:13 2015 +0100
    URL: https://www.monitoring-plugins.org/repositories/monitoring-plugin-perl/commit/?id=049e72d

Merge pull request #5 from daku3649/patch-1

output empty values as "U"

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