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I am creating a custom log4j appender (extends AppenderSkeleton) to
record data into a previous developed logging system.

On occasion (18 times out of test order 120,000 executions) (not
reproducable, as of yet), I get the following message in my log file:

>> 160954.679:Notification Processor #4:INFO
com.datamodel.WorkOrder - CANNOT PROCESS PROPERLY
java.lang.NullPointerException

>> 160954.679:Notification Processor #4:INFO
.....

the line prefixed with ">>" is the log header record.

My problem is that I do not know whether the NPE exception is generated
and reported in the appender or in the calling code; since there is no
stack trace printed.

Is there appender debugging tools or can someone offer a suggestion
here?