(node:6580) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'length' of undefined?

Question

Node.js

Help I'm trying to setinterval and getting this error

(node:6580) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'length' of undefined

setInterval(async () => {
  for (a in users) {
    for(let i = 0; i < users[a].business.length; i++)
    {
      users[a].business[i].moneys += users[a].business[i].workers
    }
  }
}, 30000);