Careful sending complex objects to lambda callback

Ran into an issue today with the following code. It's the second or third time it's bitten me, and I think this time I finally am learning the general guideline: don't pass complex objects into your lambda success/failure callbacks!

```js
export async function main(event, context, callback) {
  const id = event.pathParameters.id;
  try {
    const result = await startExecution(
      process.env.statemachine_arn, JSON.stringify({ id })
    );
    callback(null, success({ status: true, result }));
  } catch (error) {
    console.log(error.message);
    callback(error, failure({ status: false, message: error.message }));
  }
}
```
This lambda will fail with `Converting circular structure to JSON` exception, because the result object returned from the `startExecution` function is a big complex object that doesn't work with `JSON.stringify`. I've had the same thing happen to me with the results of `axios` requests, as well as other AWS service calls.

To fix, don't pass `result` but instead pass only what you need returned, or simply `true`.

obie-fernandez
February 13, 2019