ros compiles catkin_make/catkin build and reports an error "string no output variable specified"

Problem Description

CMake Error at /opt/ros/melodic/share/catkin/cmake/platform/lsb.cmake:8 (string):
  string no output variable specified
Call Stack (most recent call first):
  /opt/ros/melodic/share/catkin/cmake/all.cmake:164 (include)
  /opt/ros/melodic/share/catkin/cmake/catkinConfig.cmake:20 (include)
  CMakeLists.txt:58 (find_package)

problem analysis

The native environment of python is destroyed and lsb cannot be recognized.