Github user tison1 commented on the issue:
https://github.com/apache/flink/pull/6353
Fix unstable case, the problem is code below, that may assign `constraints`
to a long array and then to a short array, which cause out of index exception.
to solve it we could init `constraints` in object construct.
https://github.com/apache/flink/blob/056486a1b81e9648a6d3dc795e7e2c6976f8388c/flink-runtime/src/main/java/org/apache/flink/runtime/jobmanager/scheduler/CoLocationGroup.java#L87-L91---
