RLException: [demo.launch] is neither a launch file in package [panda_moveit_config] nor is [panda_moveit_config] a launch file name The traceback for the exception was written to the log file

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I've been following the MoveIt! tutorial for ROS Melodic on the MoveIt! Docs page but couldn't launch the demo.launch file with:

roslaunch panda_moveit_config demo.launch rviz_tutorial:=true

I got an exception which looks like this:

RLException: [demo.launch] is neither a launch file in package [panda_moveit_config] nor is [panda_moveit_config] a launch file name The traceback for the exception was written to the log file

With all the launch files including demo.launch in the panda_moveit_config/launch directory clearly visible, I'm surprise to still see an exception like this.

What can I do to make use of the demo.launch file.