Alex Leung created KAFKA-8671:
---------------------------------

             Summary: NullPointerException occurs if topic associated with 
GlobalKTable changes
                 Key: KAFKA-8671
                 URL: https://issues.apache.org/jira/browse/KAFKA-8671
             Project: Kafka
          Issue Type: Bug
          Components: streams
    Affects Versions: 2.0.0
            Reporter: Alex Leung


The following NullPointerException occurs when the global/.checkpoint file 
contains a line with a topic previously associated with (but no longer 
configured for) a GlobalKTable:


{code:java}
java.lang.NullPointerException
at 
org.apache.kafka.streams.processor.internals.GlobalStateUpdateTask.update(GlobalStateUpdateTask.java:85)
at 
org.apache.kafka.streams.processor.internals.GlobalStreamThread$StateConsumer.pollAndUpdate(GlobalStreamThread.java:241)
at 
org.apache.kafka.streams.processor.internals.GlobalStreamThread.run(GlobalStreamThread.java:290){code}
 

After line 84 
([https://github.com/apache/kafka/blob/2.0/streams/src/main/java/org/apache/kafka/streams/processor/internals/GlobalStateUpdateTask.java#L84)]
 `sourceNodeAndDeserializer` is null for the old, but still valid, topic. This 
can be reproduced with the following sequence:


 # create a GlobalKTable associated with topic, 'global-topic1'
 # change the topic associated with the GlobalKTable to 'global-topic2' 
 ##  at this point, the global/.checkpoint file will contain lines for both 
topics
 # produce messages to previous topic ('global-topic1')
 # the consumer will attempt to consume from global-topic1, but no deserializer 
associated with global-topic1 will be found and the NPE will occur

It looks like the following recent commit has included checkpoint validations 
that may prevent this issue: 
https://github.com/apache/kafka/commit/53b4ce5c00d61be87962f603682873665155cec4#diff-cc98a6c20f2a8483e1849aea6921c34dR425



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