Describe the bug
When fitting data using the zero fit. The line is fit to the correct values but when all value are null or undefined the line is rendered without dashes.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://codesandbox.io/s/objective-architecture-xnnvs?file=/src/App.tsx
2. Notice line is drawn as solid not dashed
3. Uncomment the fourth row of the dataset
4. Notice the line becomes dashed.

Expected behaviour
The fitted line should be dashed

Screenshots

As soon as a non-null value is added to the dataset, the line is correctly dashed.

Version (please complete the following information):

• Elastic Charts: master

Additional context
Add any other context about the problem here.