Analyse following RPM build log snippet. Describe contents accurately, without speculation or suggestions for resolution.            
Your analysis must be as concise as possible, while keeping relevant information intact.
Snippet: 
WARNING: Unexpected exception while executing onClean
java.lang.RuntimeException: Exception from cleanup action to verify if the cleaner thread would survive
	at org.postgresql.util.LazyCleanerTest.lambda$phantomCleaner$0(LazyCleanerTest.java:55)
	at org.postgresql.util.LazyCleaner$Node.onClean(LazyCleaner.java:219)
	at org.postgresql.util.LazyCleaner$1.run(LazyCleaner.java:137)
	at java.base/java.lang.Thread.run(Thread.java:840)
Unexpected exception was encountered while executing `onClean`. The exception was encountered in java code. 