Prevent NPE when attempt to fetch partition information fails

[rajagopr]

Changes are to prevent the NPE and provide a meaningful error message to the user when there is a failure to fetch the partition information.

NPE seen by the end user who created a Kafka topic without any partitions in a third-party managed Kafka cluster.

Caused by: java.lang.NullPointerException
        at org.apache.pinot.plugin.stream.kafka20.KafkaStreamMetadataProvider.fetchPartitionCount(KafkaStreamMetadataProvider.java:60) ~[startree-write-api-0.13.0-ST.98.3-shaded.jar:0.13.0-ST.98.3-1eb9c04b445be445d976f47c790dddaed274298d]
        at org.apache.pinot.spi.stream.StreamMetadataProvider.computePartitionGroupMetadata(StreamMetadataProvider.java:68) ~[startree-pinot-all-0.13.0-ST.98.3-jar-with-dependencies.jar:0.13.0-ST.98.3-1eb9c04b445be445d976f47c790dddaed274298d]
        at org.apache.pinot.spi.stream.PartitionGroupMetadataFetcher.call(PartitionGroupMetadataFetcher.java:70) ~[startree-pinot-all-0.13.0-ST.98.3-jar-with-dependencies.jar:0.13.0-ST.98.3-1eb9c04b445be445d976f47c790dddaed274298d]
        at org.apache.pinot.spi.stream.PartitionGroupMetadataFetcher.call(PartitionGroupMetadataFetcher.java:31) ~[startree-pinot-all-0.13.0-ST.98.3-jar-with-dependencies.jar:0.13.0-ST.98.3-1eb9c04b445be445d976f47c790dddaed274298d]
        at org.apache.pinot.spi.utils.retry.BaseRetryPolicy.attempt(BaseRetryPolicy.java:50) ~[startree-pinot-all-0.13.0-ST.98.3-jar-with-dependencies.jar:0.13.0-ST.98.3-1eb9c04b445be445d976f47c790dddaed274298d]
        at org.apache.pinot.controller.helix.core.PinotTableIdealStateBuilder.getPartitionGroupMetadataList(PinotTableIdealStateBuilder.java:160) ~[startree-pinot-all-0.13.0-ST.98.3-jar-with-dependencies.jar:0.13.0-ST.98.3-1eb9c04b445be445d976f47c790dddaed274298d]
        ... 31 more

Notes: Unable to add a test using mocks as the class KafkaPartitionLevelConnectionHandler declares the consumer as final within it's constructor. Additionally, the Kafka library always creates a default partition (0) when creating the Kafka topic.

[codecov-commenter]

Codecov Report

Merging #11769 (1c68b99) into master (13c2901) will decrease coverage by 0.02%.
Report is 4 commits behind head on master.
The diff coverage is 50.00%.

@@             Coverage Diff              @@
##             master   #11769      +/-   ##
============================================
- Coverage     63.13%   63.12%   -0.02%     
  Complexity     1117     1117              
============================================
  Files          2342     2342              
  Lines        125916   125920       +4     
  Branches      19370    19371       +1     
============================================
- Hits          79501    79489      -12     
- Misses        40749    40768      +19     
+ Partials       5666     5663       -3     

Flag	Coverage Δ
integration	<0.01% <0.00%> (ø)
integration1	<0.01% <0.00%> (ø)
integration2	0.00% <0.00%> (ø)
java-11	63.05% <50.00%> (-0.02%)	⬇️
java-17	62.97% <50.00%> (+0.02%)	⬆️
java-20	62.96% <50.00%> (-0.03%)	⬇️
temurin	63.12% <50.00%> (-0.02%)	⬇️
unittests	63.12% <50.00%> (-0.02%)	⬇️
unittests1	67.23% <ø> (+<0.01%)	⬆️
unittests2	14.45% <50.00%> (-0.02%)	⬇️

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

Files	Coverage Δ
...in/stream/kafka20/KafkaStreamMetadataProvider.java	44.61% <50.00%> (-0.55%)	⬇️

... and 16 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[snleee]

Is it easy to add the testing case for this?