add_custom_target(CustomTarget)
set_property(TARGET CustomTarget PROPERTY LINK_LIBRARIES)
set_property(TARGET CustomTarget APPEND PROPERTY LINK_LIBRARIES)
get_property(val TARGET CustomTarget PROPERTY LINK_LIBRARIES)
if (NOT "${val}" STREQUAL "")
  message(FATAL_ERROR "LINK_LIBRARIES value is '${val}' but should be ''")
endif()