`TypeError: o[n] is not a function` for empty color domain

[jeremy-rifkin]

I'm setting up a plot where the data set used for the plot may be empty. In such cases, I end up passing color: { legend: true, domain } where domain is an empty array but this leads to an error. Here's a demo that produces the error due to an empty data set and empty domain https://observablehq.com/d/f1142c360da5114b.

Locally I see:

TypeError: I[i2] is not a function
    piecewise piecewise.js:9
    legendRamp ramp.js:95
    legendColor legends.js:53
    createLegends legends.js:76
    plot plot.js:325
    render_chart main.ts:110
    do_query main.ts:278
    onreadystatechange utils.ts:6
    http_get utils.ts:3
    do_query main.ts:263
    query_keystroke main.ts:66
    timeoutId utils.ts:23
    setTimeout handler*debounce/< utils.ts:22
    App main.ts:33
    <anonymous> main.ts:288

[Fil]

Minimal repro: Plot.legend({color: {domain: []}}).

[Fil]

Note that you could specify type:"ordinal" to fix it.

[mbostock]

Yeah, I think the bug here is that this should be interpreted as an ordinal scale rather than a linear scale. Something here…

  // If the domain or range has more than two values, assume it’s ordinal. You
  // can still use a “piecewise” (or “polylinear”) scale, but you must set the
  // type explicitly.
  if ((domain || range || []).length > 2) return asOrdinalType(kind);