I'm trying to get SSE working, and ran into this:

ERROR i.p.http.impl.servlet-interceptor  - {:msg "Dev interceptor caught an exception;
Forwarding it as the response.", :line 314}
clojure.lang.ExceptionInfo: java.lang.IllegalArgumentException in Interceptor :io.pedes
tal.http.sse/start-event-stream41445 - No implementation of method: :exec of protocol:
#'clojure.core.async.impl.protocols/Executor found for class: clojure.core.async.impl.e
xec.threadpool$thread_pool_executor$reify__8430
        at clojure.core$ex_info.invokeStatic(core.clj:4739)
        at clojure.core$ex_info.invoke(core.clj:4739)
        at io.pedestal.interceptor.chain$throwable__GT_ex_info.invokeStatic(chain.clj:3
5)
        at io.pedestal.interceptor.chain$throwable__GT_ex_info.invoke(chain.clj:32)
        at io.pedestal.interceptor.chain$try_f.invokeStatic(chain.clj:57)
        at io.pedestal.interceptor.chain$try_f.invoke(chain.clj:44)
        at io.pedestal.interceptor.chain$process_all_with_binding.invokeStatic(
j:171)