defer the Creation of ISE, to when an exception needs to be created (Manual merge of #264)

hystrix-core/src/main/java/com/netflix/hystrix/collapser/CollapsedRequestObservableFunction.java

@@ -99,6 +99,26 @@ public void setExceptionIfResponseNotReceived(Exception e) {
         }
     }
 
+    /**
+     * Set an ISE if a response is not yet received otherwise skip it
+     *
+     * @param e A pre-generated exception.  If this is null an ISE will be created and returned
+     * @param exceptionMessage The message for the ISE
+     */
+    public Exception setExceptionIfResponseNotReceived(Exception e, String exceptionMessage) {
+        Exception exception = e;
+        CollapsedRequestObservableFunction.ResponseHolder<T> r = rh.get();
+        // only proceed if neither response is set
+        if (!r.isResponseSet() && r.getException() == null) {
+            if(e == null) {
+                exception = new IllegalStateException(exceptionMessage);
+            }
+            setExceptionIfResponseNotReceived(exception);
+        }
+        // return any exception that was generated
+        return exception;
+    }
+
     /**
      * When set any client thread blocking on get() will immediately be unblocked and receive the exception.
      * 

hystrix-core/src/main/java/com/netflix/hystrix/collapser/RequestBatch.java

@@ -143,10 +143,10 @@ public void call(Throwable e) {
                             @Override
                             public void call() {
                                 // check that all requests had setResponse or setException invoked in case 'mapResponseToRequests' was implemented poorly
-                                IllegalStateException ie = new IllegalStateException("No response set by " + commandCollapser.getCollapserKey().name() + " 'mapResponseToRequests' implementation.");
+                                Exception e = null;
                                 for (CollapsedRequest<ResponseType, RequestArgumentType> request : shardRequests) {
                                     try {
-                                        ((CollapsedRequestObservableFunction<ResponseType, RequestArgumentType>) request).setExceptionIfResponseNotReceived(ie);
+                                       e = ((CollapsedRequestObservableFunction<ResponseType, RequestArgumentType>) request).setExceptionIfResponseNotReceived(e,"No response set by " + commandCollapser.getCollapserKey().name() + " 'mapResponseToRequests' implementation.");
                                     } catch (IllegalStateException e2) {
                                         logger.debug("Partial success of 'mapResponseToRequests' resulted in IllegalStateException while setting 'No response set' Exception. Continuing ... ", e2);
                                     }