buildbot failure in ASF Buildbot on flink-docs-master

[buildbot]

The Buildbot has detected a new failure on builder flink-docs-master while 
building ASF Buildbot. Full details are available at:
    http://ci.apache.org/builders/flink-docs-master/builds/5

Buildbot URL: http://ci.apache.org/

Buildslave for this Build: hemera_ubuntu

Build Reason: The Nightly scheduler named 'flink-nightly-docs-master' triggered 
this build
Build Source Stamp: [branch master] HEAD
Blamelist: 

BUILD FAILED: failed compile

Sincerely,
 -The Buildbot