[CMake] IF(string) is false. Why?

[Brandon Van Every]

IF("WHATEVER")
  MESSAGE("WHATEVER string is true")
ELSE("WHATEVER")
  MESSAGE("WHATEVER string is false")
ENDIF("WHATEVER")

C:\devel\src\cbugs\trueorfalse>cmake -P trueorfalse.cmake
WHATEVER string is false

I would expect the literal string "WHATEVER" to evaluate to true.  By
analogy to IF(variable) as per the docs.  The practical application is
I'm trying to sanity check an argument that's a literal string.

MACRO(DOSOMETHING literal_string result)
  IF(${literal_string})
    SET(result "valid")
  ELSE(${literal_string})
    MESSAGE(SEND_ERROR "I don't like the input!")
  ENDIF(${literal_string})
ENDMACRO(DOSOMETHING)
DOSOMETHING("WHATEVER" out)

C:\devel\src\cbugs\trueorfalse>cmake -P trueorfalse.cmake
CMake Error: I don't like the input!


Cheers,
Brandon Van Every