Fetch robot simple simulation

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Hi,

I am learning how to use OpenAI-ROS package from here. I am trying to run the example of learning the object pushing task using fetch robot. For that I need to have the package fetch_simple_simulation which I have downloaded from here and the supporting package spawn_robot_tools from here. In order to check whether my simulator is running properly or not, I ran the following command

roslaunch fetch_simple_description main.launch By running the above command, I got error as No link elements found in urdf file. The complete output of the above roslaunch command is provided below. I am unable to fix the error and any help in resolving the issue will be appreciated.

I am using ROS Noetic, Ubuntu 20.04.

... logging to /home/user/.ros/log/7d7a5516-7ecc-11eb-a64c-eb44e79e9fe4/roslaunch-user-ai-15108.log
Checking log directory for disk usage. This may take a while.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.

started roslaunch server http://user-ai:43231/

SUMMARY
========

PARAMETERS
 * /fetch/bellows_joint_position_controller/joint: bellows_joint
 * /fetch/bellows_joint_position_controller/pid/d: 1000.0
 * /fetch/bellows_joint_position_controller/pid/i: 0.0
 * /fetch/bellows_joint_position_controller/pid/p: 10000.0
 * /fetch/bellows_joint_position_controller/type: effort_controller...
 * /fetch/elbow_flex_joint_position_controller/joint: elbow_flex_joint
 * /fetch/elbow_flex_joint_position_controller/pid/d: 10.0
 * /fetch/elbow_flex_joint_position_controller/pid/i: 10.0
 * /fetch/elbow_flex_joint_position_controller/pid/p: 3000.0
 * /fetch/elbow_flex_joint_position_controller/type: effort_controller...
 * /fetch/forearm_roll_joint_position_controller/joint: forearm_roll_joint
 * /fetch/forearm_roll_joint_position_controller/pid/d: 0.0
 * /fetch/forearm_roll_joint_position_controller/pid/i: 0.1
 * /fetch/forearm_roll_joint_position_controller/pid/p: 3000.0
 * /fetch/forearm_roll_joint_position_controller/type: effort_controller...
 * /fetch/head_pan_joint_position_controller/joint: head_pan_joint
 * /fetch/head_pan_joint_position_controller/pid/d: 20.0
 * /fetch/head_pan_joint_position_controller/pid/i: 0.0
 * /fetch/head_pan_joint_position_controller/pid/p: 100.0
 * /fetch/head_pan_joint_position_controller/type: effort_controller...
 * /fetch/head_tilt_joint_position_controller/joint: head_tilt_joint
 * /fetch/head_tilt_joint_position_controller/pid/d: 1.0
 * /fetch/head_tilt_joint_position_controller/pid/i: 0.0
 * /fetch/head_tilt_joint_position_controller/pid/p: 10.0
 * /fetch/head_tilt_joint_position_controller/type: effort_controller...
 * /fetch/joint_state_controller/publish_rate: 50
 * /fetch/joint_state_controller/type: joint_state_contr...
 * /fetch/l_gripper_finger_joint_position_controller/joint: l_gripper_finger_...
 * /fetch/l_gripper_finger_joint_position_controller/pid/d: 0.0
 * /fetch/l_gripper_finger_joint_position_controller/pid/i: 0.1
 * /fetch/l_gripper_finger_joint_position_controller/pid/p: 5000.0
 * /fetch/l_gripper_finger_joint_position_controller/type: effort_controller...
 * /fetch/r_gripper_finger_joint_position_controller/joint: r_gripper_finger_...
 * /fetch/r_gripper_finger_joint_position_controller/pid/d: 0.0
 * /fetch/r_gripper_finger_joint_position_controller/pid/i: 0.1
 * /fetch/r_gripper_finger_joint_position_controller/pid/p: 5000.0
 * /fetch/r_gripper_finger_joint_position_controller/type: effort_controller...
 * /fetch/shoulder_lift_joint_position_controller/joint: shoulder_lift_joint
 * /fetch/shoulder_lift_joint_position_controller/pid/d: 0.0
 * /fetch/shoulder_lift_joint_position_controller/pid/i: 0.1
 * /fetch/shoulder_lift_joint_position_controller/pid/p: 5000.0
 * /fetch/shoulder_lift_joint_position_controller/type: effort_controller...
 * /fetch/shoulder_pan_joint_position_controller/joint: shoulder_pan_joint
 * /fetch/shoulder_pan_joint_position_controller/pid/d: 200.0
 * /fetch/shoulder_pan_joint_position_controller/pid/i: 10.0
 * /fetch/shoulder_pan_joint_position_controller/pid/p: 1000.0
 * /fetch/shoulder_pan_joint_position_controller/type: effort_controller...
 * /fetch/torso_lift_joint_position_controller/joint: torso_lift_joint
 * /fetch/torso_lift_joint_position_controller/pid/d: 1000.0
 * /fetch/torso_lift_joint_position_controller/pid/i: 0.0
 * /fetch/torso_lift_joint_position_controller/pid/p: 10000.0
 * /fetch/torso_lift_joint_position_controller/type: effort_controller...
 * /fetch/upperarm_roll_joint_position_controller/joint: upperarm_roll_joint
 * /fetch/upperarm_roll_joint_position_controller/pid/d: 0.0
 * /fetch/upperarm_roll_joint_position_controller/pid/i: 0.1
 * /fetch/upperarm_roll_joint_position_controller/pid/p: 3000.0
 * /fetch/upperarm_roll_joint_position_controller/type: effort_controller...
 * /fetch/wrist_flex_joint_position_controller/joint: wrist_flex_joint
 * /fetch/wrist_flex_joint_position_controller/pid/d: 500.0
 * /fetch/wrist_flex_joint_position_controller/pid/i: 10.0
 * /fetch/wrist_flex_joint_position_controller/pid/p: 1000.0
 * /fetch/wrist_flex_joint_position_controller/type: effort_controller...
 * /fetch/wrist_roll_joint_position_controller/joint: wrist_roll_joint
 * /fetch/wrist_roll_joint_position_controller/pid/d: 500.0
 * /fetch/wrist_roll_joint_position_controller/pid/i: 0.0
 * /fetch ...