`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?

Riproduci il problema usando Figure.to_json, Figure.to_plotly_json e l’esempio del colore del marker scatter riportato nel report. Confronta questi punti di ingresso della serializzazione per determinare come viene rappresentato np.nan durante il round-trip, quindi aggiungi un test di regressione che copra il comportamento coerente previsto.