Null values with category-based Y-axis don't render correctly

[htr3n]

Version

5.1.2

Reproduction link

https://codepen.io/htr3n/pen/YzQKMrq

Steps to reproduce

1. Define a chart with the following options

• A-axis with type "category", set data to some kind of category such as ["6:00", "6:30", "7:00", "7:30"]
• Y-axis with type "category", set data to some sort of category for instance ["A", "B", "C", "D"]
• A series with a list of null input data: data: [null, null, null, null],

What is expected?

The chart should not render any values because they are all null.

What is actually happening?

The chart renders the first value at the position of the first Y-axis category.

---

Replace null with undefined, the chart seems to render correctly.

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This issue is labeled with priority: high, which means it's a frequently asked problem and we will fix it ASAP.