def get_left_table(self):
        if self.left_table:
            return self.left_table
        if len(self.owner.tables):
            return self.owner.tables[0]
get_app() returns None when loaded app is not found.
dataset/ETHPy150Open ambitioninc/django-query-builder/querybuilder/query.py/Join.get_left_table--crossover with--dataset/ETHPy150Open rapidsms/rapidsms/rapidsms/router/blocking/tests/test_app.py/RouterAppTest.test_get_invalid_app_by_path