HDFS-17107. Null Pointer Exception after turned on detail metric for namenode lock

[teamconfx]

Description of PR

https://issues.apache.org/jira/browse/HDFS-17107

This PR adds a null check for the detailedHoldTimeMetrics if the metric is enabled.

How was this patch tested?

1. Set dfs.namenode.lock.detailed-metrics.enabled=true
2. Run org.apache.hadoop.hdfs.server.namenode.TestFSNamesystemLock#testFSWriteLockReportSuppressed
   The test throws IllegalArgumentException as expected.

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 29s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 0s		codespell was not available.
+0 🆗	detsecrets	0m 0s		detect-secrets was not available.
+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	31m 38s		trunk passed
+1 💚	compile	0m 55s		trunk passed with JDK Ubuntu-11.0.20+8-post-Ubuntu-1ubuntu120.04
+1 💚	compile	0m 48s		trunk passed with JDK Private Build-1.8.0_382-8u382-ga-1~20.04.1-b05
+1 💚	checkstyle	0m 50s		trunk passed
+1 💚	mvnsite	0m 59s		trunk passed
+1 💚	javadoc	0m 50s		trunk passed with JDK Ubuntu-11.0.20+8-post-Ubuntu-1ubuntu120.04
+1 💚	javadoc	1m 9s		trunk passed with JDK Private Build-1.8.0_382-8u382-ga-1~20.04.1-b05
+1 💚	spotbugs	2m 13s		trunk passed
+1 💚	shadedclient	23m 49s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 43s		the patch passed
+1 💚	compile	0m 45s		the patch passed with JDK Ubuntu-11.0.20+8-post-Ubuntu-1ubuntu120.04
+1 💚	javac	0m 45s		the patch passed
+1 💚	compile	0m 40s		the patch passed with JDK Private Build-1.8.0_382-8u382-ga-1~20.04.1-b05
+1 💚	javac	0m 40s		the patch passed
-1 ❌	blanks	0m 0s	/blanks-eol.txt	The patch has 1 line(s) that end in blanks. Use git apply --whitespace=fix <<patch_file>>. Refer https://git-scm.com/docs/git-apply
-0 ⚠️	checkstyle	0m 33s	/results-checkstyle-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs-project/hadoop-hdfs: The patch generated 2 new + 1 unchanged - 0 fixed = 3 total (was 1)
+1 💚	mvnsite	0m 43s		the patch passed
+1 💚	javadoc	0m 37s		the patch passed with JDK Ubuntu-11.0.20+8-post-Ubuntu-1ubuntu120.04
+1 💚	javadoc	1m 4s		the patch passed with JDK Private Build-1.8.0_382-8u382-ga-1~20.04.1-b05
+1 💚	spotbugs	1m 47s		the patch passed
+1 💚	shadedclient	23m 7s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	195m 5s		hadoop-hdfs in the patch passed.
+1 💚	asflicense	0m 39s		The patch does not generate ASF License warnings.
		290m 41s

Subsystem	Report/Notes
Docker	ClientAPI=1.43 ServerAPI=1.43 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-6033/1/artifact/out/Dockerfile
GITHUB PR	#6033
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	Linux 67c8492bf3f3 4.15.0-213-generic #224-Ubuntu SMP Mon Jun 19 13:30:12 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / c01207c
Default Java	Private Build-1.8.0_382-8u382-ga-1~20.04.1-b05
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Ubuntu-11.0.20+8-post-Ubuntu-1ubuntu120.04 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_382-8u382-ga-1~20.04.1-b05
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-6033/1/testReport/
Max. process+thread count	3939 (vs. ulimit of 5500)
modules	C: hadoop-hdfs-project/hadoop-hdfs U: hadoop-hdfs-project/hadoop-hdfs
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-6033/1/console
versions	git=2.25.1 maven=3.6.3 spotbugs=4.2.2
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[github-actions]

We're closing this stale PR because it has been open for 100 days with no activity. This isn't a judgement on the merit of the PR in any way. It's just a way of keeping the PR queue manageable.
If you feel like this was a mistake, or you would like to continue working on it, please feel free to re-open it and ask for a committer to remove the stale tag and review again.
Thanks all for your contribution.