Looking at the code in powerbi-visuals-tools\lib\VisualBuilder.js, files seems to be necessary. And you may also reach out for help at github.
let apiDtsFiles = tsConfig.files.filter(i => i.match(/.api\/.+\/PowerBI-visuals.d.ts$/));
Looking at the code in powerbi-visuals-tools\lib\VisualBuilder.js, files seems to be necessary. And you may also reach out for help at github.
let apiDtsFiles = tsConfig.files.filter(i => i.match(/.api\/.+\/PowerBI-visuals.d.ts$/));