Update SocketModeFunctions.ts

[rileyeaton]

Summary

This PR will fix an issue where the bolt app will crash due to disabling socket mode while running. When this is disabled, the app crashes due to an attempt to access a key of an undefined value, body.type. All that is needed to avoid this crash is to add optional chaining.

This is the error that is displayed (locally) when socket mode is disabled:

C:\Users\RileyEaton\Documents\gameon\node_modules\@slack\bolt\dist\receivers\SocketModeFunctions.js:17
        logger.error(`An unhandled error occurred while Bolt processed (type: ${event.body.type}, error: ${error})`);
                                                                                           ^

TypeError: Cannot read properties of undefined (reading 'type')
    at SocketModeReceiver.defaultProcessEventErrorHandler [as processEventErrorHandler] (C:\Users\RileyEaton\Documents\gameon\node_modules\@slack\bolt\dist\receivers\SocketModeFunctions.js:17:92)
    at SocketModeClient.<anonymous> (C:\Users\RileyEaton\Documents\gameon\node_modules\@slack\bolt\dist\receivers\SocketModeReceiver.js:129:50)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)

This is because the event object is:

{
  body: undefined,
  ack: [AsyncFunction: ack],
  retryNum: undefined,
  retryReason: undefined,
  customProperties: {}
}

It is important that this is fixed because it cannot be caught by any users of this library as it is an internal process.

Please correct me if this pull request should be to a different base branch as I am not familiar with the current branch structure.

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[CLAassistant]

All committers have signed the CLA.

[rileyeaton]

@seratch I can't add reviewers now that I have submitted this. The maintainers (such as yourself?) will need to add them. Thanks!

[rileyeaton]

The root of this issue stems from why the body property is undefined, however, this quick fix is necessary first to stop user's applications from crashing.

[WilliamBergamin]

Hi @rileyeaton thanks for catching this and contributing!

LGTM!

[codecov]

Codecov Report

Merging #1553 (cb54385) into main (1e15a68) will decrease coverage by 0.06%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #1553      +/-   ##
==========================================
- Coverage   82.08%   82.01%   -0.07%     
==========================================
  Files          18       18              
  Lines        1496     1496              
  Branches      435      436       +1     
==========================================
- Hits         1228     1227       -1     
  Misses        172      172              
- Partials       96       97       +1     

Impacted Files	Coverage Δ
src/receivers/SocketModeFunctions.ts	88.88% <0.00%> (-11.12%)	⬇️

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