Return a Case object

            If no case_id is given return one case

            Args:
                case_id (str): A case id

            Returns:
                case(Case): A Case object

def case(self, case_id=None):
        """Return a Case object

            If no case_id is given return one case

            Args:
                case_id (str): A case id

            Returns:
                case(Case): A Case object
        """
        cases = self.cases()
        if case_id:
            for case in cases:
                if case.case_id == case_id:
                    return case
        else:
            if cases:
                return cases[0]

        return None