make aggregation step optional

src/main/java/we/fizz/Pipeline.java

@@ -95,6 +95,9 @@ public class Pipeline {
 			return Mono.just(aggregateResult);
 		}
 
+		if(CollectionUtils.isEmpty(steps)) {
+			return handleOutput(input);
+		}else {			
 			LinkedList<Step> opSteps = (LinkedList<Step>) steps.clone();
 			Step step1 = opSteps.removeFirst();
 			step1.beforeRun(stepContext, null);
@@ -107,6 +110,12 @@ public class Pipeline {
 				return createStep(step);
 			}).flatMap(response -> Flux.just(response)).collectList();
 			return result.flatMap(clientResponse -> {
+				return handleOutput(input);
+			});
+		}
+	}
+	
+	private Mono<AggregateResult> handleOutput(Input input){
 		// 数据转换
 		long t3 = System.currentTimeMillis();
 		AggregateResult aggResult = this.doInputDataMapping(input, null);
@@ -118,7 +127,6 @@ public class Pipeline {
 			LOGGER.info("stepContext {}", JSON.toJSONString(stepContext));
 		}
 		return Mono.just(aggResult);
-		});
 	}
 
 	@SuppressWarnings("unchecked")