Fix postman import with empty url

[Nikita240]

If you try importing a postman collection that contains an empty raw url, it silently fails.

Just needed a nullcheck.

[TravisBuddy]

Hey @Nikita240,
Your changes look good to me!

View build log

TravisBuddy Request Identifier: b33913b0-82c2-11ea-a3c8-5be21eefecce

[Nikita240]

Here's a sample json to test:

{
	"info": {
		"_postman_id": "f695cab7-6878-eb55-7943-ad88e1ccfd65",
		"name": "Test",
		"schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
	},
	"item": [
		{
			"name": "Test",
			"request": {
				"method": "GET",
				"header": [],
				"url": {
					"raw": ""
				}
			},
			"response": []
		}
	]
}