fix: discontinued data for line charts

[marrouchi]

Motivation

For line chart, data value could be missing (null) for a specfic range, what makes the point and lines get "0" on the Y Axis. This PR fixes that by allowing null values (scaled to undefined)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have done the work for both react and vue
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (Storybook)
• I have added unit tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes