Github user zentol commented on the issue:
https://github.com/apache/flink/pull/5959
The methods have been identical since FLINK-7692, but I didn't catch it in
the review. Thus, `ComponentMetricGroup#getAllVariables()` should be removed,
along with `ComponentMetricGroup#putVariables()`, and the fix applied to
`AbstractMetricGroup#getAllVariables()`.
We try to construct as many things as possible lazily, to reduce the
resource impact in case the metric system isn't used.---
