Setting falsy type for data serie renders data serie twice when chart type is set.

[bj00rn]

Description

Setting falsy type for data serie renders data serie twice when chart type is set.

In C3 data serie type would fall back to line

Billboard behaviour

C3 behaviour

Steps to check or reproduce

// for ESM environment, need to import modules as:
// import bb, {bar, spline, line, area, step} from "billboard.js";

var chart = bb.generate({
  data: {
    type: "bar",
    columns: [
	["data1", 30, 20, 50, 40, 60, 50],
	["data2", 200, 130, 90, 240, 130, 220],
    ],
    types: {
      data2: undefined, // "", null
    },
  },
  bindto: "#combinationChart"
});

[netil]

@bj00rn, thanks for reporting issue.
The way handling for cases specifying falsy value for data.types will not behave same way as c3.js case.

When data.types has falsy value, then will follow the data.type value, which is "parent & general concept" for types.
So, hierarchically will have below relationship.

data.type
└-- data.types

Following this definition, from the above example, data2 type will be rendered as bar.