fix null pointe exception #26

webmagic-core/src/main/java/us/codecraft/webmagic/selector/BaseElementSelector.java

@@ -2,22 +2,30 @@ package us.codecraft.webmagic.selector;
 
 import org.jsoup.Jsoup;
 
+import java.util.ArrayList;
 import java.util.List;
 
 /**
  * @author code4crafter@gmail.com
  * @since 0.3.0
  */
-public abstract class BaseElementSelector implements Selector,ElementSelector {
+public abstract class BaseElementSelector implements Selector, ElementSelector {
 
     @Override
     public String select(String text) {
-        return select(Jsoup.parse(text));
+        if (text != null) {
+            return select(Jsoup.parse(text));
+        }
+        return null;
     }
 
     @Override
     public List<String> selectList(String text) {
-        return selectList(Jsoup.parse(text));
+        if (text != null) {
+            return selectList(Jsoup.parse(text));
+        } else {
+            return new ArrayList<String>();
+        }
     }
 
 }

webmagic-extension/src/main/java/us/codecraft/webmagic/model/PageModelExtractor.java

@@ -184,7 +184,7 @@ class PageModelExtractor {
             return null;
         }
         if (objectExtractor == null) {
-            return processSingle(page, null, false);
+            return processSingle(page, null, true);
         } else {
             if (objectExtractor.multi) {
                 List<Object> os = new ArrayList<Object>();