Aws-sdk-js: getCredentials TypeScript signature is incorrect for strict mode users

[Nemikolh]

Confirm by changing [ ] to [x] below to ensure that it's a bug:

• [x] I've gone through Developer Guide and API reference
• [x] I've checked AWS Forums and StackOverflow for answers
• [x] I've searched for previous similar issues and didn't find any solution

Describe the bug

When trying to mock the implementation of getCredentials in Jest, the following code in TypeScript (using strict mode) will fail:

const impl = jest.spyOn(AWS.config, 'getCredentials').mockImplementation(
    cb => cb(null), // Argument of type 'null' is not assignable to parameter of type 'AWSError'
);

The signature of function getCredentials:

https://github.com/aws/aws-sdk-js/blob/319f32535d18003fce3bf9d103656b2defb7ff4c/lib/config.d.ts#L13

should be:

getCredentials(callback: (err: AWSError | null) => void): void;

Is the issue in the browser/Node.js?
N/A

If on Node.js, are you running this on AWS Lambda?

Details of the browser/Node.js version
N/A

SDK version number
v2.647.0
master

To Reproduce (observed behavior)

import * as AWS from 'aws-sdk';

AWS.config.getCredentials(err => {
    // In strict mode TypeScript should report an error, but doesn't because err can never be null.
    err.stack
});

Expected behavior
In the reproduce section above, you should have a TypeScript compilation error but you don't.

[ajredniwja]

@Nemikolh Thank-you for reaching out and providing the PR as well, will have someone review it soon.

[workeitel]

I think this was fixed in 89640c2f66245d2ac5a659a10c2d186e7fc87a99