From the stacktrace and some source reading, it seems clj-stacktrace
passes null as class-name in clj-stacktrace.core/clojure-ns, which
passes it to a regex function.
That should not even be possible, because it passes the same value to
clj-stacktrace.core/clojure-code?, which would already throw, a few
Also, the null value originates from StackTraceElement.getClassName()
which I'm not even sure is allowed to be null.
Maybe it was some funky state you got your JVM into. Can you reproduce