API Subscription XML Response Change

As of December 17, 2018, we have made a change to how a subscription is displayed in the XML API response.

Previously, dates and integers that had a null value still displayed its type:

<trial-started-at type=\"datetime\" nil=\"true\"/>
<next_product_id type="integer" nil="true"/>

Now, for null fields, the type is no longer returned:

<trial-started-at nil=\"true\"/>
<next_product_id nil="true"/>