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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def authenticate(self, username=None, password=None):
 """ Returns a valid `MojUser` if the authentication is successful or None if the credentials were wrong. """

        data = api_client.authenticate(username, password)
        if not data:
            return

        return User(
            data.get('pk'), data.get('token'), data.get('user_data')
        )