fix #127 (#128)

diff --git a/rocketmq-streams-commons/src/main/java/org/apache/rocketmq/streams/common/channel/impl/file/FileSource.java b/rocketmq-streams-commons/src/main/java/org/apache/rocketmq/streams/common/channel/impl/file/FileSource.java
index 2843abf..61aadd7 100644
--- a/rocketmq-streams-commons/src/main/java/org/apache/rocketmq/streams/common/channel/impl/file/FileSource.java
+++ b/rocketmq-streams-commons/src/main/java/org/apache/rocketmq/streams/common/channel/impl/file/FileSource.java
@@ -116,7 +116,7 @@
         LinkedBlockingQueue<FileIterator> iterators = new LinkedBlockingQueue<>(1000);
         File file = getFile(filePath);
         if (!file.exists()) {
-            return null;
+            throw new RuntimeException("filePath not exist.the filePath is "+filePath);
         }
         try {
             if (!file.isDirectory()) {