RejectedExecutionException? I don't think I was using anything concurrent?

[sugarste...@gmail.com]

My app starts up, runs for a few minutes, and then:

#<RejectedExecutionException java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.FutureTask@4fe887e6 rejected from java.util.concurrent.ThreadPoolExecutor@aea107f[Terminated, pool size = 0, active threads = 0, queued tasks = 0, completed tasks = 3]>

This is a very simple app, and I am not aware of using any concurrency. I am not using Futures or Promises or pmap or anything else I can think of. My first hunch would be this comes from some library I am using, but I am not sure what. I searched on Google but none of the reported problems seem to apply to me. This is what I am using, do any of these seem likely to throw this error?

[org.clojure/clojure "1.6.0"]
                 [com.taoensso/timbre "4.0.2"]
                 [dire "0.5.1"]
                 [slingshot "0.12.2"]
                 [org.clojure/data.json "0.2.5"]
                 [org.clojure/tools.namespace "0.2.4"]
             [me.raynes/fs "1.4.4"]
                 [clj-stacktrace "0.2.8"]
                 [overtone/at-at "1.2.0"]
                 [org.clojure/core.cache "0.6.4"]
                 [cheshire "5.5.0"]
                 [com.taoensso/carmine "2.11.1"]

[sugarste...@gmail.com]

Okay, this error seems to be triggered by a NullPointerException which seems to arise when I try to fetch a non-existent document out of Redis. I am a bit of a noob, so perhaps someone can explain how this works. I'm not aware of using any of Clojure's concurrency tools in this (very simple) app, so how might the NullPointerException lead to RejectedExecutionException? 

[Zach Tellman]

A RejectedExecutionException is thrown when a thread-pool's queue is full.  Try using 'jstack' to take a thread dump, and see who has spun up a thread pool under the covers.  Possible culprits include 'at-at' and 'carmine'.