Gracefully handle intermittent web3 (infura?) errors

[atvanguard]

(node:47094) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'blockNumber' of null
    at Web3Client.<anonymous> (/Users/arpit/projects/moonwalker/dist/Web3Client.js:85:33)
    at step (/Users/arpit/projects/moonwalker/dist/Web3Client.js:32:23)
    at Object.next (/Users/arpit/projects/moonwalker/dist/Web3Client.js:13:53)
    at fulfilled (/Users/arpit/projects/moonwalker/dist/Web3Client.js:4:58)
    at process.internalTickCallback (internal/process/next_tick.js:77:7)
(node:47094) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:47094) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.