How can I remove the “the Location property may no

问题:

I am now trying run a cmake script in this post. With this script CMake will print all the properties of a target. However, when it tries to retrieve the "LOCATION" property of the target, the following error is observed:

The LOCATION property may not be read from target "abc".  Use the target
  name directly with add_custom_command, or use the generator expression
  $<TARGET_FILE>, as appropriate.

Then I tried to print the property with message($<TARGET_FILE:abc>), it does not work either. Any ideas?