diff --git a/oauth2client/client.py b/oauth2client/client.py
index 71c9d81..f6f4a1a 100644
--- a/oauth2client/client.py
+++ b/oauth2client/client.py
@@ -159,7 +159,8 @@
     t = type(self)
     d = copy.copy(self.__dict__)
     for member in strip:
-      del d[member]
+      if member in d:
+        del d[member]
     if 'token_expiry' in d and isinstance(d['token_expiry'], datetime.datetime):
       d['token_expiry'] = d['token_expiry'].strftime(EXPIRY_FORMAT)
     # Add in information we will need later to reconsistitue this instance.
@@ -203,6 +204,19 @@
     from_json = getattr(kls, 'from_json')
     return from_json(s)
 
+  @classmethod
+  def from_json(cls, s):
+    """Instantiate a Credentials object from a JSON description of it. The JSON
+    should have been produced by calling .to_json() on the object.
+
+    Args:
+      data: dict, A deserialized JSON object.
+
+    Returns:
+      An instance of a Credentials subclass.
+    """
+    return Credentials()
+
 
 class Flow(object):
   """Base class for all Flow objects."""