Reduce nullity test complexity by returning empty array instead of null

Author: JeanDeboutGat

webmagic-core/src/main/java/us/codecraft/webmagic/downloader/HttpClientGenerator.java

@@ -91,7 +91,7 @@ public void checkServerTrusted(X509Certificate[] chain, String authType) throws
 
             @Override
             public X509Certificate[] getAcceptedIssuers() {
-                return null;
+            	return new X509Certificate[0];
             }
 
         };