Github user mwws commented on the issue:
https://github.com/apache/flink/pull/2179
Yes, I am also confused about why it can compile before. But according to
[archived flink-dev
mail](http://mail-archives.apache.org/mod_mbox/flink-dev/201506.mbox/%3CCAJLORfdqMsJdNricb8WDSBrNWPzgAD=oqdWned1cL3KFB+i+=g...@mail.gmail.com%3E)
Some people do have the same issue as me.
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