diff --git a/src/main/java/com/qiniu/pili/Hub.java b/src/main/java/com/qiniu/pili/Hub.java
index b1af3df..a8ed072 100644
--- a/src/main/java/com/qiniu/pili/Hub.java
+++ b/src/main/java/com/qiniu/pili/Hub.java
@@ -71,7 +71,7 @@ public Stream get(String streamKey) throws PiliException {
     }
 
     private ListRet list(boolean live, String prefix, int limit, String marker) throws PiliException {
-        String path = String.format("%s/streams?liveonly=%s&prefix=%s&limit=%d&marker=%s", baseUrl, live, prefix, limit, marker);
+        String path = String.format("%s/streams?liveonly=%s&prefix=%s&limit=%d&marker=%s", baseUrl, live, nullToEmpty(prefix), limit, nullToEmpty(marker));
         try {
             String resp = cli.callWithGet(path);
 
@@ -92,6 +92,13 @@ private ListRet list(boolean live, String prefix, int limit, String marker) thro
 
     }
 
+    private String nullToEmpty(String str) {
+        if (str == null) {
+            return "";
+        }
+        return str;
+    }
+
     /**
      * list stream
      *