cmake_minimum_required(VERSION 3.1)

message("CMake version: ${CMAKE_VERSION}")
set(d "")

message("Quoted test")
if("d" STREQUAL "")
  message("Surprise!")
else()
  message("OK")
endif()

message("Unquoted test")
if(d STREQUAL "")
  message("Surprise!")
else()
  message("OK")
endif()