Fix option promises include empty file

slapos/recipe/cmmi/__init__.py

@@ -29,7 +29,7 @@ class Recipe(object):
         else:
             self.original_options = options.copy()
             options.update(platform_options)
-
+        
         options['location'] = os.path.join(
             buildout['buildout']['parts-directory'],
             self.name)
@@ -185,7 +185,7 @@ class Recipe(object):
     def check_promises(self, log=None):
         result = True
         log = logging.getLogger(self.name)
-        for path in self.options['promises'].splitlines():
+        for path in filter(None, self.options['promises'].splitlines()):
             if not os.path.exists(path):
                 result = False
                 log.warning('could not find promise "%s"' % path)