From f39aa435cfc3758921eba038743adadd65566fab Mon Sep 17 00:00:00 2001
From: "yihua.huang" <code4crafter@gmail.com>
Date: Wed, 16 Apr 2014 19:46:32 +0800
Subject: [PATCH] add null check #104

---
 .../src/main/java/us/codecraft/webmagic/Spider.java       | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/webmagic-core/src/main/java/us/codecraft/webmagic/Spider.java b/webmagic-core/src/main/java/us/codecraft/webmagic/Spider.java
index c9b1dd7..6d436bd 100644
--- a/webmagic-core/src/main/java/us/codecraft/webmagic/Spider.java
+++ b/webmagic-core/src/main/java/us/codecraft/webmagic/Spider.java
@@ -187,9 +187,11 @@ public class Spider implements Runnable, Task {
         checkIfRunning();
         Scheduler oldScheduler = this.scheduler;
         this.scheduler = scheduler;
-        Request request;
-        while ((request = oldScheduler.poll(this)) != null) {
-            this.scheduler.push(request, this);
+        if (oldScheduler != null) {
+            Request request;
+            while ((request = oldScheduler.poll(this)) != null) {
+                this.scheduler.push(request, this);
+            }
         }
         return this;
     }