Not all promises are rejected with errors

[air2]

I noticed some calls are rejected with 'FAILED_TO_VERIFY_SIGNATURE' not an Error object. So in flow.ts I see code like: return Promise.reject('FAILED_TO_VERIFY_SIGNATURE');

IMHO Promises should ALWAYS be rejected with errors, although this is of course not a requirement I think it is good practice. There is linting available to enforce this.