Merge pull request #4 from sysprog21/fix_preprocessor_expanded_empty

Check empty strings on macro expansion

kconfiglib.py

@@ -2612,7 +2612,7 @@ def _parse_assignment(self, s):
             else:
                 break
 
-        if s.isspace():
+        if not s or s.isspace():
             # We also accept a bare macro on a line (e.g.
             # $(warning-if,$(foo),ops)), provided it expands to a blank string
             return