fixed: headers can be nil

@@ -43,7 +43,7 @@
       (doseq [val val-or-vals]
         (.addHeader response key val))))
   ; Some headers must be set through specific methods
-  (when-let [content-type (headers "Content-Type")]
+  (when-let [content-type (get headers "Content-Type")]
     (.setContentType response content-type))
   ; Apply the body - the method depends on the given body type.
   (cond