Add check for missing block data to gas-oracle

[vponline]

This fixes a bug where block is null (or undefined) which causes the gas oracle to fail with an unexpected error stopping the Airseeker and adds tests for this case.

{
    "errorType": "Runtime.UnhandledPromiseRejection",
    "errorMessage": "TypeError: Cannot read property 'transactions' of null",
    "reason": {
        "errorType": "TypeError",
        "errorMessage": "Cannot read property 'transactions' of null",
        "stack": [
            "TypeError: Cannot read property 'transactions' of null",
            "    at /var/task/dist/gas-oracle.js:118:54",
            "    at Array.reduce (<anonymous>)",
            "    at /var/task/dist/gas-oracle.js:115:61",
            "    at step (/var/task/dist/gas-oracle.js:44:23)",
            "    at Object.next (/var/task/dist/gas-oracle.js:25:53)",
            "    at fulfilled (/var/task/dist/gas-oracle.js:16:58)",
            "    at processTicksAndRejections (internal/process/task_queues.js:95:5)"
        ]
    },
    "promise": {},
    "stack": [
        "Runtime.UnhandledPromiseRejection: TypeError: Cannot read property 'transactions' of null",
        "    at process.<anonymous> (/var/runtime/index.js:35:15)",
        "    at process.emit (events.js:400:28)",
        "    at process.emit (domain.js:475:12)",
        "    at processPromiseRejections (internal/process/promises.js:245:33)",
        "    at processTicksAndRejections (internal/process/task_queues.js:96:32)"
    ]
}

[aquarat]

I think there's a bigger issue here and that is that a bug in this component caused the Airseeker execution to end.

I think it might be a good idea to add an error check/try-catch around:
in https://github.com/API3-CTT/airseeker/blob/46f87c8b02b5207277cd2bc91a6a73b04f353699/src/update-beacons.ts#L185
with a fallback to conventional pricing.

We should expect EVM RPC endpoints to give us unexpected data because (1) good practice to expect the worst and (2) we're operating across under-served chains with new implementations.

Also, separately, we may want to add import 'source-map-support/register'; to this application to make debugging in future easier. Size won't be an issue because we're running it ourselves.

(I didn't realise Github could quote lines inline like this^, cool!)

[vponline]

I think it might be a good idea to add an error check/try-catch around:

Thanks for checking and good catch @aquarat !

Could this be wrapped in a go-function with 0 retries? I'm asking because I just finished a task to replace all try-catches in Airnode with promise-utils go? I'm not sure if there are any plans to replace try-catches here, though.

[aquarat]

Could this be wrapped in a go-function with 0 retries? I'm asking because I just finished a task to replace all try-catches in Airnode with promise-utils go?

I really like the go utils approach to error handling... it's very C/Go like and satisfies @Siegrift 's suggestion of keeping "unhappy paths" indented and the happy path as left as possible. I say great idea :)

[Siegrift]

Also, separately, we may want to add import 'source-map-support/register'; to this application to make debugging in future easier. Size won't be an issue because we're running it ourselves.

I think this is something we should consider for all Airnode, Airkeeper and Airseeker in the future.

[vponline]

Ok I've done a bit of a refactor, here are the additions:

1. added source-map-support/register
2. extracted fallback gas price fetching into a new function: getFallbackGasPrice
3. added go-wrapper and fallback gas price logic to update-beacons.ts if getOracleGasPrice fails
4. added tests for the above

Please let me know what you think.

[aquarat]

See comment 😄

[aquarat]

This is really neat 🥇 (and I think it'll be both efficient and robust).
Thanks again 😄