diff --git a/hgext/convert/common.py b/hgext/convert/common.py
--- a/hgext/convert/common.py
+++ b/hgext/convert/common.py
@@ -17,7 +17,7 @@ class converter_source(object):
     def __init__(self, ui, path, rev=None):
         """Initialize conversion source (or raise NoRepo("message")
         exception if path is not a valid repository)"""
-        raise NotImplementedError()
+        pass
 
     def getheads(self):
         """Return a list of this repository's heads"""
diff --git a/hgext/convert/cvs.py b/hgext/convert/cvs.py
--- a/hgext/convert/cvs.py
+++ b/hgext/convert/cvs.py
@@ -7,6 +7,8 @@ from common import NoRepo, commit, conve
 
 class convert_cvs(converter_source):
     def __init__(self, ui, path, rev=None):
+        super(convert_cvs, self).__init__(ui, path, rev=rev)
+
         self.path = path
         self.ui = ui
         self.rev = rev
diff --git a/hgext/convert/git.py b/hgext/convert/git.py
--- a/hgext/convert/git.py
+++ b/hgext/convert/git.py
@@ -9,6 +9,8 @@ class convert_git(converter_source):
         return os.popen('GIT_DIR=%s %s' % (self.path, s))
 
     def __init__(self, ui, path, rev=None):
+        super(convert_git, self).__init__(ui, path, rev=rev)
+
         if os.path.isdir(path + "/.git"):
             path += "/.git"
         if not os.path.exists(path + "/objects"):
diff --git a/hgext/convert/subversion.py b/hgext/convert/subversion.py
--- a/hgext/convert/subversion.py
+++ b/hgext/convert/subversion.py
@@ -77,6 +77,8 @@ class svn_paths(object):
 # SVN conversion code stolen from bzr-svn and tailor
 class convert_svn(converter_source):
     def __init__(self, ui, url, rev=None):
+        super(convert_svn, self).__init__(ui, url, rev=rev)
+
         try:
             SubversionException
         except NameError: