Vega-lite : scale(null) produces wrong vega code; scale": {"type": null} ist not correct and not identical to scale: null

[mubu-med]

Best Example is from https://haifengl.github.io/vegalite.html: A Bar Chart Encoding Color Names in the Data

var bar = new View("Bar Chart Encoding Color Names in the Data");
bar.data().values("""
[
{"color": "red", "b": 28},
{"color": "green", "b": 55},
{"color": "blue", "b": 43}
]""");

bar.mark("bar");
bar.encode("x", "color").type("nominal");
bar.encode("y", "b").type("quantitative");
bar.encode("color", "color").type("nominal").scale(null);

Expected behavior
compiled with Java 21.0.5; JSON modified from "View Source" from the presented html file in FireFox 133.03
{
"$schema": "https://vega.github.io/schema/vega-lite/v5.json",
"config": {"view": {"continuousWidth": 400, "continuousHeight": 400}},
"title": "Bar Chart Encoding Color Names in the Data",
"data": {
"values": "[\n {"color": "red", "b": 28},\n {"color": "green", "b": 55},\n {"color": "blue", "b": 43}\n]"
},
"mark": {"type": "bar"},
"encoding": {
"x": {"field": "color", "type": "nominal"},
"y": {"field": "b", "type": "quantitative"},
"color": {"field": "color", "type": "nominal", "scale": null}
}

Actual behavior
compiled with Java 21.0.5 and JSON copied from "View Source" from the presented html file in FireFox 133.03

{
"$schema": "https://vega.github.io/schema/vega-lite/v5.json",
"config": {"view": {"continuousWidth": 400, "continuousHeight": 400}},
"title": "Bar Chart Encoding Color Names in the Data",
"data": {
"values": "[\n {"color": "red", "b": 28},\n {"color": "green", "b": 55},\n {"color": "blue", "b": 43}\n]"
},
"mark": {"type": "bar"},
"encoding": {
"x": {"field": "color", "type": "nominal"},
"y": {"field": "b", "type": "quantitative"},
"color": {"field": "color", "type": "nominal", "scale": {"type": null}}
}

Result is: Color will be treated as nominal - and not as color information.

The legend is displayed. This is also a clear indication that scale=null is not being interpreted.
I suspect the error in VegaLite.html respectively in ObjectNode.toPrettyString.
Unfortunately, I am only an amateur programmer and therefore could not narrow down the cause more precisely.
But thank you very much for this outstanding project!

Additional context

• What Java (OpenJDK, Orack JDK, etc.) are you using and which Java version: 21.0.5
• Which Smile version: 4.0.0
• What is your build system (e.g. Ubuntu, macOS, Windows, Debian ) : Windows 11, Eclipse 2024-12
• Add any other context about the problem here.

[kklioss]

Thanks for reporting. The fix is in v4 branch. Please have a try.