rosbridge_server - cant publish std_msgs/String

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im getting:

[INFO] [rosbridge_websocket]: Client disconnected. 0 clients total.
[INFO] [rosbridge_websocket]: Client connected. 1 clients total.
[ERROR] [rosbridge_websocket]: [Client 1] [id: advertise:/my_publisher:0] advertise: std_msgs/String is not a valid type string

im using exactly the same code from the readme page:

Ros ros = new Ros("localhost");
ros.connect();
Topic echo = new Topic(ros, "/echo", "std_msgs/String");
Message toSend = new Message("{\"data\": \"hello, world!\"}");
echo.publish(toSend);

My Configuration: ROS: ros-dashing

Client Lib: from Here (im running Client lib on an Android device)