Allow user to list projects without owner name

Change-Id: Ie03f0ca2e2e0c13335828073517d87f172215609

Author: cornmonster

odps-sdk/odps-sdk-core/src/main/java/com/aliyun/odps/Projects.java

@@ -189,21 +189,13 @@ private void updateProject(final String projectName, final Project.Status status
    *
    */
   public Iterator<Project> iterator(String owner) {
-    if (StringUtils.isNullOrEmpty(owner)) {
-      throw new IllegalArgumentException("Owner cannot be null or empty.");
-    }
-
     return new ProjectListIterator(owner, null, null);
   }
 
   /**
    * 获取 Project 列表的 iterable 接口
    */
   public Iterable<Project> iterable(final String owner) {
-    if (StringUtils.isNullOrEmpty(owner)) {
-      throw new IllegalArgumentException("Owner cannot be null or empty.");
-    }
-
     return new Iterable<Project>() {
       @Override
       public Iterator<Project> iterator() {