HDFS-17099. Fix Null Pointer Exception when stop namesystem in HDFS.

[teamconfx]

Description of PR

https://issues.apache.org/jira/browse/HDFS-17099
This PR adds a null check for getFSImage().editLog before calling updateLastAppliedTxIdFromWritten.

How was this patch tested?

(1) Set dfs.namenode.top.windows.minutes to 37914516,32,0
(2) Run test: org.apache.hadoop.hdfs.server.namenode.TestNameNodeHttpServerXFrame#testSecondaryNameNodeXFrame
The test no longer throws NullPointerException and throws the IllegalArgumentException instead, which is 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 37s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 1s		codespell was not available.
+0 🆗	detsecrets	0m 1s		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	43m 16s		trunk passed
+1 💚	compile	1m 26s		trunk passed with JDK Ubuntu-11.0.20+8-post-Ubuntu-1ubuntu120.04
+1 💚	compile	1m 24s		trunk passed with JDK Private Build-1.8.0_382-8u382-ga-1~20.04.1-b05
+1 💚	checkstyle	1m 15s		trunk passed
+1 💚	mvnsite	1m 28s		trunk passed
+1 💚	javadoc	1m 11s		trunk passed with JDK Ubuntu-11.0.20+8-post-Ubuntu-1ubuntu120.04
+1 💚	javadoc	1m 43s		trunk passed with JDK Private Build-1.8.0_382-8u382-ga-1~20.04.1-b05
+1 💚	spotbugs	3m 19s		trunk passed
+1 💚	shadedclient	35m 53s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	1m 13s		the patch passed
+1 💚	compile	1m 17s		the patch passed with JDK Ubuntu-11.0.20+8-post-Ubuntu-1ubuntu120.04
+1 💚	javac	1m 17s		the patch passed
+1 💚	compile	1m 11s		the patch passed with JDK Private Build-1.8.0_382-8u382-ga-1~20.04.1-b05
+1 💚	javac	1m 11s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	1m 1s		the patch passed
+1 💚	mvnsite	1m 18s		the patch passed
+1 💚	javadoc	0m 56s		the patch passed with JDK Ubuntu-11.0.20+8-post-Ubuntu-1ubuntu120.04
+1 💚	javadoc	1m 31s		the patch passed with JDK Private Build-1.8.0_382-8u382-ga-1~20.04.1-b05
+1 💚	spotbugs	3m 12s		the patch passed
+1 💚	shadedclient	35m 38s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
-1 ❌	unit	222m 47s	/patch-unit-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in the patch passed.
+1 💚	asflicense	0m 58s		The patch does not generate ASF License warnings.
		363m 54s

Reason	Tests
Failed junit tests	hadoop.hdfs.TestReconstructStripedFileWithRandomECPolicy

Subsystem	Report/Notes
Docker	ClientAPI=1.43 ServerAPI=1.43 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-6034/1/artifact/out/Dockerfile
GITHUB PR	#6034
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	Linux 1697749dbca2 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 / 63986b2
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-6034/1/testReport/
Max. process+thread count	3557 (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-6034/1/console
versions	git=2.25.1 maven=3.6.3 spotbugs=4.2.2
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[Hexiaoqiao]

LGTM. +1 from my side. Will commit if no other comments for two work days.

[ayushtkn]

LGTM

[teamconfx]

Hi @ayushtkn @Hexiaoqiao, are we able to merge this PR if it looks good to you? ;)

[Hexiaoqiao]

Sorry for too late to push forward this PR.
Committed to trunk. Thanks @teamconfx and @ayushtkn