Error when deleting a charge

[DavidVII]

Hello, I got an error when deleting a charge. It appears that the request to cancel works, but the parse_json/2 function in the Response module throws an error.

Shopify.RecurringApplicationCharge.delete(session, 1234)
> no case clause matching: {:error, :invalid, 0}
    (shopify) lib/shopify/response.ex:24: Shopify.Response.parse_json/2
    (shopify) lib/shopify/response.ex:12: Shopify.Response.new/3

It appears that parse_json is being called with the following arguments: parse_json(nil, "")

nil being the resource, and "" is the body.

This results in the following being called here:

Poison.decode("", as: nil)
> {:error, :invalid, 0}

You'll notice the result there is the same as my error above. I'm happy to take a stab at a PR for this, but I'm curious how we might want to handle the response here?

There's no response body from Shopify according to their docs. This seems inconsistent with other DELETE calls where the response body is an empty JSON object.

[Ninigi]

The API is full of inconsistencies, so I am not really surprised ;)
I guess we could just pattern match here and replace empty strings with an empty json object.