what is the meaning of 'system_lib', which is in the CMakeLists.txt of line 125 under the event-detector directory.

[Zhihao-Li-ai]

there is a warning when i catkin_make the project:

Make Warning at /opt/ros/noetic/share/catkin/cmake/catkin_package.cmake:166 (message):
catkin_package() DEPENDS on 'system_lib' but neither
'system_lib_INCLUDE_DIRS' nor 'system_lib_LIBRARIES' is defined.
Call Stack (most recent call first):
/opt/ros/noetic/share/catkin/cmake/catkin_package.cmake:102 (_catkin_package)
event-detector/CMakeLists.txt:113 (catkin_package)

looking forward to your reply very much