HADOOP-17468. NullPointerException from register in MetricsSystemImpl

[symious]

https://issues.apache.org/jira/browse/HADOOP-17468

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 31s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
-1 ❌	test4tests	0m 0s		The patch doesn't appear to include any new or modified tests. Please justify why no new tests are needed for this patch. Also please list what manual steps were performed to verify this patch.
			_ trunk Compile Tests _
+1 💚	mvninstall	33m 9s		trunk passed
+1 💚	compile	20m 7s		trunk passed with JDK Ubuntu-11.0.9.1+1-Ubuntu-0ubuntu1.18.04
+1 💚	compile	17m 23s		trunk passed with JDK Private Build-1.8.0_275-8u275-b01-0ubuntu1~18.04-b01
+1 💚	checkstyle	0m 54s		trunk passed
+1 💚	mvnsite	1m 31s		trunk passed
+1 💚	shadedclient	18m 9s		branch has no errors when building and testing our client artifacts.
+1 💚	javadoc	1m 5s		trunk passed with JDK Ubuntu-11.0.9.1+1-Ubuntu-0ubuntu1.18.04
+1 💚	javadoc	1m 37s		trunk passed with JDK Private Build-1.8.0_275-8u275-b01-0ubuntu1~18.04-b01
+0 🆗	spotbugs	2m 19s		Used deprecated FindBugs config; considering switching to SpotBugs.
+1 💚	findbugs	2m 17s		trunk passed
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 54s		the patch passed
+1 💚	compile	19m 16s		the patch passed with JDK Ubuntu-11.0.9.1+1-Ubuntu-0ubuntu1.18.04
+1 💚	javac	19m 16s		the patch passed
+1 💚	compile	17m 27s		the patch passed with JDK Private Build-1.8.0_275-8u275-b01-0ubuntu1~18.04-b01
+1 💚	javac	17m 27s		the patch passed
+1 💚	checkstyle	0m 54s		the patch passed
+1 💚	mvnsite	1m 31s		the patch passed
+1 💚	whitespace	0m 0s		The patch has no whitespace issues.
+1 💚	shadedclient	15m 29s		patch has no errors when building and testing our client artifacts.
+1 💚	javadoc	1m 3s		the patch passed with JDK Ubuntu-11.0.9.1+1-Ubuntu-0ubuntu1.18.04
+1 💚	javadoc	1m 36s		the patch passed with JDK Private Build-1.8.0_275-8u275-b01-0ubuntu1~18.04-b01
+1 💚	findbugs	2m 21s		the patch passed
			_ Other Tests _
+1 💚	unit	17m 28s		hadoop-common in the patch passed.
+1 💚	asflicense	0m 56s		The patch does not generate ASF License warnings.
		178m 11s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-2644/1/artifact/out/Dockerfile
GITHUB PR	#2644
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient findbugs checkstyle
uname	Linux 042dd76a773e 4.15.0-60-generic #67-Ubuntu SMP Thu Aug 22 16:55:30 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / d820095
Default Java	Private Build-1.8.0_275-8u275-b01-0ubuntu1~18.04-b01
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Ubuntu-11.0.9.1+1-Ubuntu-0ubuntu1.18.04 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_275-8u275-b01-0ubuntu1~18.04-b01
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-2644/1/testReport/
Max. process+thread count	3011 (vs. ulimit of 5500)
modules	C: hadoop-common-project/hadoop-common U: hadoop-common-project/hadoop-common
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-2644/1/console
versions	git=2.17.1 maven=3.6.0 findbugs=4.0.6
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