Merge branch 'fix-use-ctk-for-ctkexample'

* fix-use-ctk-for-ctkexample:
  Fix UseCTK.cmake to work for very simple project

CMake/UseCTK.cmake.in

@@ -30,7 +30,9 @@ if(NOT CTK_USE_FILE_INCLUDED)
   # Add include directories needed to use CTK.
   get_directory_property(existing_include_directories INCLUDE_DIRECTORIES)
   set(new_include_directories ${CTK_INCLUDE_DIRS})
-  list(REMOVE_ITEM new_include_directories ${existing_include_directories})
+  if(existing_include_directories)
+    list(REMOVE_ITEM new_include_directories ${existing_include_directories})
+  endif()
   include_directories(${new_include_directories})
 
   if (NOT DEFINED QT_QMAKE_EXECUTABLE)