Bug/2361: Retrieve broken when shared data extensions are inaccessible

[justinjxzhang]

PR details

There is a possibility during Folder's retrieve that there are no results at all (see the issue for example XML). There's an expectation for this to exist, but as it doesn't, the value of the property is undefined which leads to an error Cannot read property 'map' of undefined

What changes did you make? (Give an overview)

• Closes issue [BUG] Retrieve broken when shared data extensions are inaccessible #2361
• Add a test case with the expected (empty) response
• Null coalesces response.Results in Folder's retrieve as it may be undefined, and subsequent usage of the value throws an error.

Further details (optional)

...

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• test scripts updated
• Wiki updated (if applicable)

The base branch was changed.