KAFKA-15218: Avoid NPE thrown while deleting topic and fetch from follower concurrently

core/src/main/scala/kafka/cluster/Partition.scala

@@ -998,7 +998,14 @@ class Partition(val topicPartition: TopicPartition,
       // 3. Its metadata cached broker epoch matches its Fetch request broker epoch. Or the Fetch
       //    request broker epoch is -1 which bypasses the epoch verification.
       case kRaftMetadataCache: KRaftMetadataCache =>
-        val storedBrokerEpoch = remoteReplicasMap.get(followerReplicaId).stateSnapshot.brokerEpoch
+        val mayBeReplica = getReplica(followerReplicaId)
+        // The topic is already deleted and we don't have any replica information. In this case, we can return false
+        // so as to avoid NPE
+        if (mayBeReplica.isEmpty) {
+          warn(s"The replica state of replica ID:[$followerReplicaId] doesn't exist in the leader node. It might because the topic is already deleted.")
+          return false
+        }
+        val storedBrokerEpoch = mayBeReplica.get.stateSnapshot.brokerEpoch
         val cachedBrokerEpoch = kRaftMetadataCache.getAliveBrokerEpoch(followerReplicaId)
         !kRaftMetadataCache.isBrokerFenced(followerReplicaId) &&
           !kRaftMetadataCache.isBrokerShuttingDown(followerReplicaId) &&

core/src/test/scala/unit/kafka/cluster/PartitionTest.scala

@@ -37,7 +37,7 @@ import org.apache.kafka.metadata.LeaderRecoveryState
 import org.junit.jupiter.api.Assertions._
 import org.junit.jupiter.api.Test
 import org.mockito.ArgumentMatchers
-import org.mockito.ArgumentMatchers.{any, anyString}
+import org.mockito.ArgumentMatchers.{any, anyBoolean, anyInt, anyLong, anyString}
 import org.mockito.Mockito._
 import org.mockito.invocation.InvocationOnMock
 
@@ -55,7 +55,7 @@ import org.apache.kafka.server.common.MetadataVersion.IBP_2_6_IV0
 import org.apache.kafka.server.metrics.KafkaYammerMetrics
 import org.apache.kafka.server.util.{KafkaScheduler, MockTime}
 import org.apache.kafka.storage.internals.epoch.LeaderEpochFileCache
-import org.apache.kafka.storage.internals.log.{AppendOrigin, CleanerConfig, EpochEntry, FetchIsolation, FetchParams, LogAppendInfo, LogDirFailureChannel, LogReadInfo, LogStartOffsetIncrementReason, ProducerStateManager, ProducerStateManagerConfig}
+import org.apache.kafka.storage.internals.log.{AppendOrigin, CleanerConfig, EpochEntry, FetchIsolation, FetchParams, LogAppendInfo, LogDirFailureChannel, LogOffsetMetadata, LogReadInfo, LogStartOffsetIncrementReason, ProducerStateManager, ProducerStateManagerConfig}
 import org.junit.jupiter.params.ParameterizedTest
 import org.junit.jupiter.params.provider.ValueSource
 
@@ -1290,6 +1290,56 @@ class PartitionTest extends AbstractPartitionTest {
     )
   }
 
+  @Test
+  def testIsReplicaIsrEligibleWithEmptyReplicaMap(): Unit = {
+    val mockMetadataCache = mock(classOf[KRaftMetadataCache])
+    val partition = spy(new Partition(topicPartition,
+      replicaLagTimeMaxMs = Defaults.ReplicaLagTimeMaxMs,
+      interBrokerProtocolVersion = interBrokerProtocolVersion,
+      localBrokerId = brokerId,
+      () => defaultBrokerEpoch(brokerId),
+      time,
+      alterPartitionListener,
+      delayedOperations,
+      mockMetadataCache,
+      logManager,
+      alterPartitionManager))
+
+    when(offsetCheckpoints.fetch(ArgumentMatchers.anyString, ArgumentMatchers.eq(topicPartition)))
+      .thenReturn(None)
+    val log = logManager.getOrCreateLog(topicPartition, topicId = None)
+    seedLogData(log, numRecords = 6, leaderEpoch = 4)
+
+    val controllerEpoch = 0
+    val leaderEpoch = 5
+    val remoteBrokerId = brokerId + 1
+    val replicas = List[Integer](brokerId, remoteBrokerId).asJava
+
+    partition.createLogIfNotExists(isNew = false, isFutureReplica = false, offsetCheckpoints, None)
+
+    val initializeTimeMs = time.milliseconds()
+    assertTrue(partition.makeLeader(
+      new LeaderAndIsrPartitionState()
+        .setControllerEpoch(controllerEpoch)
+        .setLeader(brokerId)
+        .setLeaderEpoch(leaderEpoch)
+        .setIsr(List[Integer](brokerId).asJava)
+        .setPartitionEpoch(1)
+        .setReplicas(replicas)
+        .setIsNew(true),
+      offsetCheckpoints, None), "Expected become leader transition to succeed")
+
+    doAnswer(_ => {
+      // simulate topic is deleted at the moment
+      partition.delete()
+      val replica = new Replica(remoteBrokerId, topicPartition)
+      partition.updateFollowerFetchState(replica, mock(classOf[LogOffsetMetadata]), 0, initializeTimeMs, 0, 0)
+      mock(classOf[LogReadInfo])
+    }).when(partition).fetchRecords(any(), any(), anyLong(), anyInt(), anyBoolean(), anyBoolean())
+
+    assertDoesNotThrow(() => fetchFollower(partition, replicaId = remoteBrokerId, fetchOffset = 3L))
+  }
+
   @Test
   def testInvalidAlterPartitionRequestsAreNotRetried(): Unit = {
     val log = logManager.getOrCreateLog(topicPartition, topicId = None)