Serverless.com - throws error for sync lambda

[subzero10]

What are the steps to reproduce this issue?

1. Create a serverless project
2. Create a simple synchronous handler that returns 200 (no callback, no async/await)
3. Wrap handler with Honeybadger.lambdaHandler
4. Do sls deploy

What happens?

Honeybadger client throws error.

What were you expecting to happen?

Should not throw error.

Any logs, error output, etc?

TypeError: handler(...).then is not a function
    at [NODE_MODULES]/@honeybadger-io/js/dist/server/honeybadger.js:1153:26
    at async_hooks.js:304:14
    at AsyncResource.runInAsyncScope (async_hooks.js:189:9)
    at AsyncLocalStorage.run (async_hooks.js:302:35)
    at [NODE_MODULES]/@honeybadger-io/js/dist/server/honeybadger.js:1149:40
    at new Promise (<anonymous>)
    at wrappedLambdaHandler ([NODE_MODULES]/@honeybadger-io/js/dist/server/honeybadger.js:1148:16)
    at Runtime.handler ([PROJECT_ROOT]/serverless_sdk/index.js:24:10716)
    at Runtime.handleOnce (/var/runtime/Runtime.js:66:25)

Any other comments?

The issue goes away if I use async/await.

What versions are you using?

Operating System: AWS Lambda - nodejs v12
Package Version: v4.1.0
Browser Version: n/a

[subzero10]

This happens because we wanted to keep the same lambda handler definition as the handler we are wrapping:

• for async / promise-based handlers, we wrap them to a promise-based handler
• for callback-based handlers, we wrap them to a callback-based handler

In order to achieve this, we have to deduce the type of the handler and the way we do that is not 100% consistent: we simply check the number of parameters of the handler. If there are more than two, we assume it's a callback-based handler (with event, context and callback) otherwise we assume it's an async/promise-based handler. This check though does not cover the case where we have a synchronous handler that returns immediately (i.e. parameters are 2 or less and it does not return a promise).
This PR handles this case and wraps these handlers into promise-based handlers.