Caused by: java.util.ConcurrentModificationException
	at java.base/java.util.LinkedHashMap$LinkedHashIterator.nextNode(Unknown Source)
	at java.base/java.util.LinkedHashMap$LinkedKeyIterator.next(Unknown Source)
	at java.base/java.util.Iterator.forEachRemaining(Unknown Source)
	at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Unknown Source)
	at java.base/java.util.stream.ReferencePipeline$Head.forEach(Unknown Source)
	at java.base/java.util.stream.ReferencePipeline$7$1.accept(Unknown Source)
	at java.base/java.util.stream.ReferencePipeline$2$1.accept(Unknown Source)
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(Unknown Source)
	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(Unknown Source)
	at java.base/java.util.stream.AbstractPipeline.copyInto(Unknown Source)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(Unknown Source)
	at java.base/java.util.stream.AbstractPipeline.evaluate(Unknown Source)
	at java.base/java.util.stream.AbstractPipeline.evaluateToArrayNode(Unknown Source)
	at java.base/java.util.stream.ReferencePipeline.toArray(Unknown Source)
	at java.base/java.util.stream.ReferencePipeline.toArray(Unknown Source)
	at java.base/java.util.stream.ReferencePipeline.toList(Unknown Source)
	at org.springframework.kafka.listener.ConcurrentMessageListenerContainer.getAssignedPartitions(ConcurrentMessageListenerContainer.java:161)
	...

// It is imperative that the user manually synchronize on the returned map 
// when traversing any of its collection views via Iterator, Spliterator or Stream:

   Map m = Collections.synchronizedMap(new HashMap());
       ...
   Set s = m.keySet();  // Needn't be in synchronized block
       ...
   synchronized (m) {  // Synchronizing on m, not s!
       Iterator i = s.iterator(); // Must be in synchronized block
       while (i.hasNext())
           foo(i.next());
   }