I am getting while launching my turtlebot pn RVIZ

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I am using turtlebot for my obstacle avoid robot using ultrasonic sensors.I am using 8 ultrasonic sensors.I dont know where the error is but ths it is successfully seen in gazebo but while I am launching it in rviz. `[ERROR] [1596993808.761522983]: Failed to build tree: parent link [base_footprint] of joint [sonar_front_joint] not found. This is not valid according to the URDF spec. Every link you refer to from a joint needs to be explicitly defined in the robot description. To fix this problem you can either remove this joint [sonar_front_joint] from your urdf file, or add "<link name="base_footprint"/>" to your urdf file. [robot_state_publisher-3] process has died [pid 4060, exit code 255, cmd /opt/ros/kinetic/lib/robot_state_publisher/state_publisher __name:=robot_state_publisher __log:=/home/lekhasree/.ros/log/09d44e52-da65-11ea-afc1-e8d0fc91b2fd/robot_state_publisher-3.log]. log file: /home/lekhasree/.ros/log/09d44e52-da65-11ea-afc1-e8d0fc91b2fd/robot_state_publisher-3*.log

PLese help me out with this error

The urdf file is https://github.com/Lekha03/urdf-of-ul...link text.

In this I have included some files which i have been using. the turtelbot desription file is same file which is given in rospackage.