Return empty array on empty collection request response

[MichaelBelgium]

Closes #46

Stumbled on the same issue so might aswel try to fix it.

It was odd I have to do

$response = $this->graph->createCollectionRequest("GET", $endpoint)
                        ->setReturnType(User::class)
                        ->execute();

if(!is_array($users)) {

}

and not

$response = $this->graph->createCollectionRequest("GET", $endpoint)
                        ->setReturnType(User::class)
                        ->execute();

if(count($response) == 0) {}
//or
if(empty($response)) {}

[msftclas]

All CLA requirements met.

[MIchaelMainer]

Your change makes sense. We can't take it at this time as it would break folks. I will leave this PR open so that we can take this when the time comes for us to break things.

Thank you very much for putting in your effort and time into this PR!

908760

[guilliamxavier]

@MIchaelMainer: #260 would fix the bug without breaking existing code, could you please give it a look?
Edit: I just required a review directly on the PR (didn't know about that GitHub functionality)