Make sure parsed body is an array when expecting Sequence

[joheredi]

Issue:

When an operation spec defines that a response should be of type Sequence (array) but the service actually returns null/undefined instead of an empty list, we end up crashing with the following error as the empty response body gets deserialized as {}

TypeError: (_response.parsedBody || []).slice is not a function at flattenResponse (/mnt/c/Users/jepri/scratch/node_modules/@azure/ms-rest-js/dist/msRest.node.js:3518:62)
at /mnt/c/Users/jepri/scratch/node_modules/@azure/ms-rest-js/dist/msRest.node.js:3353:47
at at process._tickCallback (internal/process/next_tick.js:189:7)

See Azure/azure-sdk-for-js/issues/8445

Note: [...(_response.parsedBody || [])] gets compiled into (_response.parsedBody || []).slice().

Fix:
When we are expecting an array, make sure we have one before proceeding

[sasathy1]

Hi. Thanks for this PR. Getting this PR checked in will definitely help us achieve better availability. We are seeing dips in our service availability due to this issue. It would be really great to see this checked in sooner.
Any idea on what is the estimated time to complete this PR? Also can we get a point of contact person to reach out to in case of future inquiries?

[ramya-rao-a]

@sasathy1 Can you share which package are you using where you are seeing the issues that would be solved with this PR?

[joheredi]

/azp run public.Azure.ms-rest-js - test dependent projects

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[sasathy1]

@sasathy1 Can you share which package are you using where you are seeing the issues that would be solved with this PR?

We are using @azure/arm-eventhub and @azure/arm-servicebus(both are of version 3.2.0).

[joheredi]

/azp run public.Azure.ms-rest-js - test dependent projects

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[ramya-rao-a]

Looks like we have a new error?

[joheredi]

/azp run public.Azure.ms-rest-js - test dependent projects

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).