/** Removes last step request. */
 void removeStepRequest() {
   if (stepRequest != null) {
     requestManager.deleteEventRequest(stepRequest);
     stepRequest = null;
   }
   if (findSourceMER != null) {
     requestManager.deleteEventRequest(findSourceMER);
     findSourceMER = null;
   }
   if (findSourceSR != null) {
     requestManager.deleteEventRequest(findSourceSR);
     findSourceSR = null;
   }
 }