Q update your applications domain classes to use collections where it's appropriate. The item object MUST support all of these use cases. The application MUST use a collection.
e.g., where you have one-to-many relationships
Create unit tests for the new functionality
These are the use cases that the application will support
Title: Create a main list
Description: A user will be able to create a parent list within the application
Title: Create list items
Description: The user will be able to create items under a parent list
Title: Check off items
Description: A user will be able to check of to do list items that have been completed
Title: Edit a list item
Description: A user will be able to edit an existing list item
Title: Delete a list item
Description: A user will be able to remove / delete a list item
Title: Email list
Description: A user will be able to email a to do list to a user via email