[GitHub] [pulsar] massakam opened a new pull request #5408: [pulsar-broker] Fix bug that namespace policies does not take effect due to NPE

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massakam opened a new pull request #5408: [pulsar-broker] Fix bug that namespace policies does not take effect due to NPE
URL: https://github.com/apache/pulsar/pull/5408
 
 
   ### Motivation
   
   When produce/consume permissions for a role on a namespace are revoked, producers and consumers connected to the topic under the namespace using that role should be disconnected from the broker. However, I noticed that producers/consumers can stay connected in some topics even if the permissions are revoked.
   
   As a result of the investigation, I found that NPE was thrown in the following line:
   https://github.com/apache/pulsar/blob/094ebf7af8d0bb27bd9df3bcea2dba4e9ba204fc/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentTopic.java#L273
   
   In subscriptions that consumer has never connected to since the broker started, the dispatcher has not been initialized, so `subscription.getDispatcher()` returns null.
   
   As a result, the process of `PersistentTopic#onPoliciesUpdate()` is aborted.
   https://github.com/apache/pulsar/blob/094ebf7af8d0bb27bd9df3bcea2dba4e9ba204fc/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentTopic.java#L1668-L1682
   
   ### Modifications
   
   Before calling a dispatcher method, make sure that the dispatcher is not null.

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