diff --git a/doc/ReferenceOfApis.md b/doc/ReferenceOfApis.md
index ce01775c..e44c9182 100644
--- a/doc/ReferenceOfApis.md
+++ b/doc/ReferenceOfApis.md
@@ -62,15 +62,15 @@ API `/legacy/issues/search/:owner/:repository/:state/:keyword`
 * GET: `Repository.search_issues`
 
 API `/legacy/repos/search/:keyword`
-==============================================================
+===================================
 * GET: `Github.search_repos`
 
 API `/legacy/user/search/:keyword`
-==============================================================
+==================================
 * GET: `Github.search_users`
 
 API `/legacy/user/email/:email`
-==============================================================
+===============================
 * GET: `Github.search_user_by_email`
 
 API `/networks/:user/:repo/events`
diff --git a/doc/ReferenceOfClasses.md b/doc/ReferenceOfClasses.md
index 485c5348..bbf95b53 100644
--- a/doc/ReferenceOfClasses.md
+++ b/doc/ReferenceOfClasses.md
@@ -27,7 +27,7 @@ Methods
 * `get_user( login )`: `NamedUser`
 * `get_organization( login )`: `Organization`
 * `get_gist( id )`: `Gist`
-    * `id`: integer
+    * `id`: string
 * `get_gists()`: iterator of `Gist`
 * `search_repos( keyword )`: iterator of `Repository`
 * `legacy_search_repos( keyword, [language] )`: iterator of `Repository`
diff --git a/github/Github.py b/github/Github.py
index 3b388512..7aaedc8a 100644
--- a/github/Github.py
+++ b/github/Github.py
@@ -31,8 +31,9 @@ class Github( object ):
     def rate_limiting( self ):
         return self.__requester.rate_limiting
 
-    def get_user( self, login = None ):
-        if login is None:
+    def get_user( self, login = GithubObject.NotSet ):
+        assert login is GithubObject.NotSet or isinstance( login, ( str, unicode ) ), login
+        if login is GithubObject.NotSet:
             return AuthenticatedUser.AuthenticatedUser( self.__requester, { "url": "https://api.github.com/user" }, completed = False )
         else:
             headers, data = self.__requester.requestAndCheck(
@@ -44,6 +45,7 @@ class Github( object ):
             return NamedUser.NamedUser( self.__requester, data, completed = True )
 
     def get_organization( self, login ):
+        assert isinstance( login, ( str, unicode ) ), login
         headers, data = self.__requester.requestAndCheck(
             "GET",
             "https://api.github.com/orgs/" + login,
@@ -53,9 +55,10 @@ class Github( object ):
         return Organization.Organization( self.__requester, data, completed = True )
 
     def get_gist( self, id ):
+        assert isinstance( id, ( str, unicode ) ), id
         headers, data = self.__requester.requestAndCheck(
             "GET",
-            "https://api.github.com/gists/" + str( id ),
+            "https://api.github.com/gists/" + id,
             None,
             None
         )