`to_json` does not handle color as `np.nan` properly

When creating a scatter plot with colors including np.nan the figure shows fine.

import json
import numpy as np
import plotly.graph_objects as go

go.Figure(go.Scatter(x=[0, 0], y=[0, 1], marker={"color": [0, np.nan]}))

However, if I convert the figure to JSON and load it back, there will be an error.

fig = go.Figure(go.Scatter(x=[0, 0], y=[0, 1], marker={"color": [0, np.nan]}))
go.Figure(**json.loads(fig.to_json()))

Error message:

ValueError: 
    Invalid element(s) received for the 'color' property of scatter.marker
        Invalid elements include: [None]

    The 'color' property is a color and may be specified as:
      - A hex string (e.g. '#ff0000')
      - An rgb/rgba string (e.g. 'rgb(255,0,0)')
      - An hsl/hsla string (e.g. 'hsl(0,100%,50%)')
      - An hsv/hsva string (e.g. 'hsv(0,100%,100%)')
      - A named CSS color:
            aliceblue, antiquewhite, aqua, aquamarine, azure,
            beige, bisque, black, blanchedalmond, blue,
            blueviolet, brown, burlywood, cadetblue,
            chartreuse, chocolate, coral, cornflowerblue,
            cornsilk, crimson, cyan, darkblue, darkcyan,
            darkgoldenrod, darkgray, darkgrey, darkgreen,
            darkkhaki, darkmagenta, darkolivegreen, darkorange,
            darkorchid, darkred, darksalmon, darkseagreen,
            darkslateblue, darkslategray, darkslategrey,
            darkturquoise, darkviolet, deeppink, deepskyblue,
            dimgray, dimgrey, dodgerblue, firebrick,
            floralwhite, forestgreen, fuchsia, gainsboro,
            ghostwhite, gold, goldenrod, gray, grey, green,
            greenyellow, honeydew, hotpink, indianred, indigo,
            ivory, khaki, lavender, lavenderblush, lawngreen,
            lemonchiffon, lightblue, lightcoral, lightcyan,
            lightgoldenrodyellow, lightgray, lightgrey,
            lightgreen, lightpink, lightsalmon, lightseagreen,
            lightskyblue, lightslategray, lightslategrey,
            lightsteelblue, lightyellow, lime, limegreen,
            linen, magenta, maroon, mediumaquamarine,
            mediumblue, mediumorchid, mediumpurple,
            mediumseagreen, mediumslateblue, mediumspringgreen,
            mediumturquoise, mediumvioletred, midnightblue,
            mintcream, mistyrose, moccasin, navajowhite, navy,
            oldlace, olive, olivedrab, orange, orangered,
            orchid, palegoldenrod, palegreen, paleturquoise,
            palevioletred, papayawhip, peachpuff, peru, pink,
            plum, powderblue, purple, red, rosybrown,
            royalblue, rebeccapurple, saddlebrown, salmon,
            sandybrown, seagreen, seashell, sienna, silver,
            skyblue, slateblue, slategray, slategrey, snow,
            springgreen, steelblue, tan, teal, thistle, tomato,
            turquoise, violet, wheat, white, whitesmoke,
            yellow, yellowgreen
      - A number that will be interpreted as a color
        according to scatter.marker.colorscale
      - A list or array of any of the above

Interestingly, the to_plotly_json method works fine:

fig = go.Figure(go.Scatter(x=[0, 0], y=[0, 1], marker={"color": [0, np.nan]}))
go.Figure(**json.loads(json.dumps(fig.to_plotly_json())))

Questions: Is this the expected behavior for the to_json method, and why it behaves differently from the to_plotly_json method?

Tái hiện vấn đề bằng Figure.to_json, Figure.to_plotly_json và ví dụ về màu của marker scatter trong báo cáo. So sánh các điểm vào serialization này để xác định np.nan được biểu diễn như thế nào trong quá trình round-trip, sau đó thêm một regression test bao phủ hành vi nhất quán dự kiến.