CMAKE_SYSTEM_VERSION is set to "nothing" when no <WindowsTargetPlatformVersion> defined in vcxproj/props

[bigla]

I get

set(CMAKE_SYSTEM_VERSION  CACHE TYPE INTERNAL FORCE)

in the root CMakeLists.txt when converting a solution where no (sub-)projects or props define

  <PropertyGroup Label="Globals">
    <WindowsTargetPlatformVersion>8.1</WindowsTargetPlatformVersion>
  </PropertyGroup>

according to CMake Doc
CMAKE_SYSTEM_VERSION is by default set to the same value as the CMAKE_HOST_SYSTEM_VERSION

a comment in related CMake Issue #16713 says
CMAKE_SYSTEM_VERSION should be available in your CMakeLists.txt since it can be a hard requirement for compiling.

So if I understand it correctly
set(CMAKE_SYSTEM_VERSION CACHE TYPE INTERNAL FORCE)
should either not exist or be
set(CMAKE_SYSTEM_VERSION ${CMAKE_HOST_SYSTEM_VERSION} CACHE TYPE INTERNAL FORCE)
in the CMakeLists.txt when there is no Version available to set.