buildbot failure in on flink-statefun-docs-master

[buildbot]

The Buildbot has detected a new failure on builder flink-statefun-docs-master 
while building . Full details are available at:
    https://ci.apache.org/builders/flink-statefun-docs-master/builds/20

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

Buildslave for this Build: bb_slave2_ubuntu

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

BUILD FAILED: failed Build docs

Sincerely,
 -The Buildbot