.

src/main/java/org/b3log/solo/service/UserMgmtService.java

@@ -172,7 +172,7 @@ public class UserMgmtService {
             }
 
             final String userName = requestJSONObject.optString(User.USER_NAME);
-            if (UserExt.invalidUserName(userName)) {
+            if (StringUtils.isEmpty(userName)) {
                 throw new ServiceException(langPropsService.get("userNameInvalidLabel"));
             }