Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://codesandbox.io/s/eloquent-wildflower-lovci?file=/src/App.tsx
2. Mouse over the column b,c the tooltip should not show the null b value and should not show the missing c value for the b series.
3. Remove the stackMode and verify that the b and c bars tooltip correctly hides the missing/null values.

Expected behaviour

In both, percentage mode and stacked mode, the tooltip should reflect the actual values:

• if the value is a valid number, it should be shown
• if the value is null or undefined no value should be shown

Screenshots

normally stacked

percentage stacked

Version (please complete the following information):

• Elastic Charts: > 33.0.0

Additional context
Add any other context about the problem here.

Errors in browser console
If applicable, add any console error.