simplify apply_requires

tiramisu/setting.py

@@ -624,17 +624,20 @@ class Settings(object):
         :param path: the option's path in the config
         :type path: str
         """
-        if opt.impl_getrequires() == []:
-            return frozenset()
+        current_requires = opt.impl_getrequires()
 
         # filters the callbacks
         if debug:
             calc_properties = {}
         else:
             calc_properties = set()
+
+        if not current_requires:
+            return calc_properties
+
         context = self._getcontext()
         all_properties = None
-        for requires in opt.impl_getrequires():
+        for requires in current_requires:
             for require in requires:
                 option, expected, action, inverse, \
                     transitive, same_action = require