incorrect continous color mapping on maps if min and max is same

[dirslashls]

Version

5.0.0

Steps to reproduce

Navigate to https://echarts.apache.org/examples/en/editor.html?c=map-usa

Change the visualMap and data options to the following and leave the rest as is.

1. visualMap options

       visualMap: {
            left: 'right',
            min: 4822023,
            max: 4822023,
            inRange: {
                color: ['#313695', '#4575b4', '#74add1', '#abd9e9', '#e0f3f8', '#ffffbf', '#fee090', '#fdae61', '#f46d43', '#d73027', '#a50026']
            },
            text: ['High', 'Low'],           // 文本，默认为数值文本
            calculable: true
        },

2. series data options

                data:[
                    {name: 'Alabama', value: 4822023},
                ]

What is expected?

Expect to see only the single state with data to have the color.

What is actually happening?

Entire map has the same color including the state with the data.

---

If I set the min and max to be different values, the coloring works fine. However, in my case the min/max are automatically calculated based on the data and if there is data for a single state, this happens.

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[Ovilia]

I think in this case, the last color should be used instead of the center one, similar to the case of degenerated CSS gradient.

This will make the gradient look like a solid-color image equal to the color of the last color-stop, ...

[pissang]

I think the main issue here is only Alabama should be expected to have color. But instead, all regions have colors now when min, max is same.

[Ovilia]

@pissang is right. I took the demo as piecewise visualMap by mistake.