Problem when instantiating Tasks in the tableauserver when they have no Schedule assigned #1290

Describe the bug
In our Tableau Site we don't use schedules for tasks, and when trying to fetch the issues from the endpoint, it fails.

Versions
Details of your environment, including:

• Tableau Server Online
• Python 3.9
• TSC library version v0.28

To Reproduce
In a server without Schedules, try to get tasks with, for example:
req_option = tsc.RequestOptions(pagesize=1000) all_extracts, pagination_item = server.tasks.get(req_option)

Results
It fails because there is no name for schedules.

NOTE: Be careful not to post user names, passwords, auth tokens or any other private or sensitive information.

The solution is to make the schedule optional for the tasks, as those can be created without schedules.