const packageJsonFile = await(files
        .filter(name => name.match(/package\.json/gi)) // ['file 1', 'file 2', 'file 3'] or []
        .filter((_, index) => index === 0) // ['file 1'] or []
        .map(name => danger.git.JSONDiffForFile(name)) // [Promise] or []
        .find((_, index) => index === 0) || Promise.resolve(null)); // Promise