Hidi: Filtering OpenAPI spec by Postman collection fails #1342

Describe the bug

Filtering OpenAPI spec by a Postman collection fails with the following error:

Could not transform the document, reason: Object reference not set to an instance of an object.

To Reproduce

• Download Graph openapi.yaml
• Create a Postman collection with some endpoint
• hidi transform -d openapi.yaml -c collection.json --co

Expected behavior

Filtered collection

Screenshots/Code Snippets

Additional context
Error is caused by a null reference here:

This stems from initializing the requestUrls as null here:

To fix this, we'd need to instantiate requestUrls as an empty Dictionary. If you're okay with this proposal I'd be happy to submit a PR.