Error while running joint_state_publisher

edit

Hi, I have been trying to bring up the joint state publisher through the launch file using the below command:

<node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher" output="screen">
   <rosparam param="source_list">[joint_states]</rosparam>
   <rosparam param="use_gui">FALSE</rosparam>
</node>`

I get the following error:

Traceback (most recent call last):

File "/opt/ros/hydro/lib/joint_state_publisher/joint_state_publisher", line 327, in <module>
    jsp = JointStatePublisher()

File "/opt/ros/hydro/lib/joint_state_publisher/joint_state_publisher", line 25, in __init__

robot = xml.dom.minidom.parseString(description).getElementsByTagName('robot')[0]

File "/usr/lib/python2.7/xml/dom/minidom.py", line 1930, in parseString
    return expatbuilder.parseString(string)

File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 940, in parseString
    return builder.parseString(string)

File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 223, in parseString
    parser.Parse(string, True)

TypeError: must be string or read-only buffer, not None



[joint_state_publisher-7] process has died [pid 6443, exit code 1, cmd /opt/ros/hydro/lib/joint_state_publisher/joint_state_publisher __name:=joint_state_publisher __log:=/home/asimov3/.ros/log/474b6a1a-3077-11e5-9d8c-e8de270f798c/joint_state_publisher-7.log].
log file: /home/asimov3/.ros/log/474b6a1a-3077-11e5-9d8c-e8de270f798c/joint_state_publisher-7*.log

Could anyone please clarify why this error is thrown?