human
Solve the following python programming problem given the following code:
def commit(self, message, author, parents = None, branch = None, date = None, **kwargs) : 
    '
        Performs in-memory commit (doesn\'t check workdir in any way) and
        returns newly created ``Changeset``. Updates repository\'s
        ``revisions``.

        :param message: message of the commit
        :param author: full username, i.e. "Joe Doe <joe.doe@example.com>"
        :param parents: single parent or sequence of parents from which commit
          would be derieved
        :param date: ``datetime.datetime`` instance. Defaults to
          ``datetime.datetime.now()``.
        :param branch: branch name, as string. If none given, default backend\'s
          branch would be used.

        :raises ``CommitError``: if any error occurs while committing
        ' 
    self.check_integrity (parents) 
    from.repository import MercurialRepository 
    if ((not isinstance (message, unicode)) or (not isinstance (author, unicode))) : 
        raise RepositoryError (('Given message and author needs to be an <unicode> instance got %r & %r instead' % (type (message), type (author)))) 
if (self is None) : 
        branch = MercurialRepository.DEFAULT_BRANCH_NAME 
kwargs ['branch'] = branch 
    def filectxfn(_repo, memctx, path) : 
        '
            Marks given path as added/changed/removed in a given _repo. This is
            for internal mercurial commit function.
            ' 
        if (path in (node.path for node in self.removed)) : 
            raise IOError (errno.ENOENT, ('%s is deleted' % path)) 
for node in self.added : 
            if (node.path == path) : 
                return memfilectx (path = node.path, data = (node.content.encode ('utf8') if (not node.is_binary) else node.content), islink = False, isexec = node.is_executable, copied = False) 
for node in self.changed : 
            if (node.path == path) : 
                return memfilectx (path = node.path, data = (node.content.encode ('utf8') if (not node.is_binary) else node.content), islink = False, isexec =...

    
    

    Fix the buggy line: if (self is None) :
assistant
#Here is Python program to fix the buggy line: if (self is None) :
.

if (branch is None) :