[PR] fix: guard NPE in TopicRouteWrapper when brokerName is absent from the route [rocketmq]

["yyqdbngt (via GitHub)" <gi...@apache.org>]

yyqdbngt opened a new pull request, #10744:
URL: https://github.com/apache/rocketmq/pull/10744

   ### Motivation
   
   `TopicRouteWrapper.getMasterAddr` and `getMasterAddrPrefer` called `brokerNameRouteData.get(brokerName).getBrokerAddrs()` without a null check. When `brokerName` is not present in the current route snapshot (e.g. during broker failover, or a stale `MessageQueue` referencing a broker no longer in the route), `get(brokerName)` returns `null` and the chained `getBrokerAddrs()` throws `NullPointerException`.
   
   This contradicts the contract the callers rely on. In `MessageQueueSelector.buildRead`/`buildWrite` and `ClusterTopicRouteService`, every call site checks the return value for `null` and skips the broker:
   
   ```java
   String brokerAddr = topicRoute.getMasterAddr(qd.getBrokerName());
   if (brokerAddr == null) {
       continue;
   }
   ```
   
   So these methods are *supposed* to return `null` for a missing broker, but instead they throw. The fix guards the lookup and returns `null`, making the existing caller handling work as intended.
   
   ### Verification
   
   `mvn -pl proxy -am compile` passes on the build server.
   
   ### Diff
   
   1 file changed, +10 / -2.


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