[improve][cli] Fix NPE in admin-CLI topic stats command

[vineeth1995]

Motivation

The admin stats command throws NullPointerException when fetching stats for a topic. This PR aims to fix the issue

Stacktrace:

sudo cloud-messaging-admin persistent stats persistent://sessionsearch-k8s/global/search_history/get
java.lang.NullPointerException
at org.apache.pulsar.admin.cli.CmdPersistentTopics$GetStats.run(CmdPersistentTopics.java:349)
at org.apache.pulsar.admin.cli.CmdBase.run(CmdBase.java:87)
at org.apache.pulsar.admin.cli.PulsarAdminTool.run(PulsarAdminTool.java:290)
at org.apache.pulsar.admin.cli.PulsarAdminTool.main(PulsarAdminTool.java:339)

Modifications

Get persistentTopics exclusively if the value is Null.

Verifying this change

This change is already covered by existing tests, such as PulsarAdminToolTest.persistentTopics().

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

[codecov-commenter]

Codecov Report

Merging #18326 (e09a80a) into master (2e878e8) will increase coverage by 6.06%.
The diff coverage is 66.66%.

@@             Coverage Diff              @@
##             master   #18326      +/-   ##
============================================
+ Coverage     40.04%   46.11%   +6.06%     
- Complexity     8625     8934     +309     
============================================
  Files           687      608      -79     
  Lines         67436    58071    -9365     
  Branches       7221     6054    -1167     
============================================
- Hits          27007    26781     -226     
+ Misses        37411    28275    -9136     
+ Partials       3018     3015       -3     

Flag	Coverage Δ
unittests	46.11% <66.66%> (+6.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ervice/persistent/MessageRedeliveryController.java	51.21% <ø> (-9.76%)	⬇️
...ulsar/utils/ConcurrentBitmapSortedLongPairSet.java	57.40% <ø> (-1.86%)	⬇️
...ersistentStickyKeyDispatcherMultipleConsumers.java	39.90% <33.33%> (-17.79%)	⬇️
...sistent/PersistentDispatcherMultipleConsumers.java	48.75% <75.00%> (-2.40%)	⬇️
...broker/delayed/InMemoryDelayedDeliveryTracker.java	65.00% <100.00%> (ø)
...g/apache/pulsar/client/impl/RawBatchConverter.java	3.12% <0.00%> (-89.07%)	⬇️
.../transaction/buffer/metadata/AbortTxnMetadata.java	28.57% <0.00%> (-57.15%)	⬇️
...lsar/broker/service/StickyKeyConsumerSelector.java	50.00% <0.00%> (-50.00%)	⬇️
...apache/pulsar/broker/service/TopicListService.java	10.65% <0.00%> (-44.27%)	⬇️
...ion/buffer/metadata/TransactionBufferSnapshot.java	42.85% <0.00%> (-42.86%)	⬇️
... and 308 more