Clojure/Java: Prevent Exceptions With “trace missing”

The other day I got this little helpful exception from Clojure:

(cond (>= nil 1) :unreachable)
;=> NullPointerException [trace missing]

– no line number or anything to troubleshoot it.

It turns out it is not Clojure’s failure but a HotSpot optimization that can apply to NullPointerException, ArithmeticException, ArrayIndexOutOfBoundsException, ArrayStoreException, and ClassCastException. The remedy is to run the JVM with

-XX:-OmitStackTraceInFastThrow

From Oralce JDK release notes:

The compiler in the server VM now provides correct stack backtraces for all “cold” built-in exceptions. For performance purposes, when such an exception is thrown a few times, the method may be recompiled. After recompilation, the compiler may choose a faster tactic using preallocated exceptions that do not provide a stack trace. To disable completely the use of preallocated exceptions, use this new flag: -XX:-OmitStackTraceInFastThrow.

Many thanks to Ivan Kozik for the info!