Question about handling of CMAKE_PREFIX_PATH

[mvieth]

Hi, I have a question about the handling of CMAKE_PREFIX_PATH: https://github.com/ros/catkin/blob/a31d8899b2567fe89173c2d0f49b7c66da803f91/cmake/all.cmake#L42-L55 At the beginning, it is tested whether CMAKE_PREFIX_PATH is not defined. We discovered a problem in perception_pcl (https://github.com/ros-perception/perception_pcl/issues/351) where CMAKE_PREFIX_PATH is defined, but empty. For details, please see there. This problem is fixed now in perception_pcl (at least for ROS 1), but it could potentially appear similarly for other ROS packages, so I wanted to notify you of this behaviour and ask, why it was written this way