variable not set in FindNetCDF.cmake

I ran the library as implemented in the upcoming mhm branch on MacOS. I got an error at here: CMake Error at cmake/cmake-modules/FindNetCDF.cmake:241 (add_library): add_library called with IMPORTED argument but no library type.

So the variable _library_type was not set. This is only possible if NetCDF_${comp}_LIBRARY is not set at line 204 and only implicitly at lines 216ff. Only then, the code in lines 239 ff. is executed.