Issue Summary

If a Work Item Milestone does not have a date set (and is not in a completed state), the roadmap header timeline across the top will no longer be visible (after refreshing the Roadmap).

Steps to Reproduce

1. Create an Epic work item (feature or capability are also possible).
2. Go to the Milestone tab of the Epic
3. Create a new milestone without any dates and save
   
4. Go to the roadmap
5. Click on the 'Milestones and Objective' button
6. Toggle 'ON' the "Milestones' and Apply
   

Expected Results

The roadmap refreshes and the timeline across the top remains.
Although the milestone requires a start or due date to display on the roadmap, the fact that they don't have any date should not affect the header of the timeline.

Actual Results

The timeline across the top goes away/disappears

When inspecting the Web browser developer tools console, we see the following warning and error:

Workaround

Make sure to set dates (start or due date) for your milestones or change the state to 'Completed'.