ROS启动rviz的时候出现这个提示是怎么回事？

ROS启动rviz的时候出现这个提示是怎么回事？

process[car/robot_state_publisher-3]: started with pid [27159]
Traceback (most recent call last):
  File "/opt/ros/melodic/lib/joint_state_publisher/joint_state_publisher", line 44, in <module>
    jsp = joint_state_publisher.JointStatePublisher()
  File "/opt/ros/melodic/lib/python2.7/dist-packages/joint_state_publisher/__init__.py", line 145, in __init__
    raise RuntimeError('The robot_description parameter is required and not set.')