nyc merge in nyc@next gives 'Invalid file coverage object, missing keys, found:data'

Link to bug demonstration repository

git clone https://github.com/akoidan/vue-webpack-typescript
git checkout multicov
yarn install
yarn test

Expected Behavior

• tests are merged, no errors

Observed Behavior

commands in example will run multiple test and then tries to run nyc merge that would fail with error: 'Invalid file coverage object, missing keys, found:data' To be specific

yarn run test:unit
yarn nyc merge ./nyc/.nyc_output_unit/ ./nyc/.nyc_output/unit.json 

results a json like this:

{
  "/home/andrew/WebstormProjects/vue-webpack-typescript/src/utils/classComponentHooks.ts": {
    "data": {
      "path": "/home/andrew/WebstormProjects/vue-webpack-typescript/src/utils/classComponentHooks.ts",
      "statementMap": {
        "0": {
          "start": {
            "line": 4,
            "column": 0
          },
          "end": {
            "line": 8,
            "column": 3
          }
        }
      },
      "fnMap": {},
      "branchMap": {},
      "s": {
        "0": 0
      },
      "f": {},
      "b": {},
      "all": true
    }
  }
}

Environment Information

npx: installed 1 in 0.76s

  System:
    OS: Linux 5.3 Arch Linux undefined
    CPU: (8) x64 Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz
    Memory: 5.92 GB / 31.25 GB
  Binaries:
    Node: 12.13.0 - /usr/bin/node
    Yarn: 1.19.1 - /usr/bin/yarn
    npm: 6.12.1 - /usr/bin/npm
  npmPackages:
    @babel/plugin-proposal-class-properties: 7.7.0 => 7.7.0 
    @babel/plugin-proposal-decorators: 7.7.0 => 7.7.0 
    @babel/preset-env: 7.7.1 => 7.7.1 
    babel-loader: 8.0.6 => 8.0.6 
    babel-plugin-istanbul: 5.2.0 => 5.2.0 
    babel-preset-typescript-vue: 1.0.2 => 1.0.2 
    istanbul-lib-coverage: 2.0.5 => 2.0.5 
    nyc: ^15.0.0-beta.0 => 15.0.0-beta.0 
    source-map-support: 0.5.16 => 0.5.16 
    ts-node: 8.5.2 => 8.5.2 
    typescript: 3.7.2 => 3.7.2