Simplify PreparedRequest.prepare API

Do not require that hooks be passed as an empty list to
PreparedRequest.prepare. In the event hooks is None in prepare or
prepare_hooks, use an empty list as a default.

Related to psf#2552

requests/models.py

@@ -523,6 +523,10 @@ def prepare_cookies(self, cookies):
 
     def prepare_hooks(self, hooks):
         """Prepares the given hooks."""
+        # hooks can be passed as None to the prepare method and to this
+        # method. To prevent iterating over None, simply use an empty list
+        # if hooks is False-y
+        hooks = hooks or []
         for event in hooks:
             self.register_hook(event, hooks[event])
 

test_requests.py

@@ -1613,7 +1613,6 @@ def test_prepare_unicode_url():
     p.prepare(
         method='GET',
         url=u('http://www.example.com/üniçø∂é'),
-        hooks=[]
     )
     assert_copy(p, p.copy())