[EAGLE-1029] fix bug in generateGroupbyMonitorMetadata

https://issues.apache.org/jira/browse/EAGLE-1029

Author: Zhao, Qingwen <qingwzhao@apache.org>

Closes #939 from qingwen220/EAGLE-1029.

(cherry picked from commit 1fb60cc762da24625f37c599c2ea89d693adad67)
Signed-off-by: Zhao, Qingwen <qingwzhao@apache.org>
3 files changed