Fixed: Donation data in Registrations endpoint

Donation data had not been populating within the Registrations endpoint with null values returned.

This issue has been fixed with data for donation_id and donation_amountnow being populated as expected in the Registrations endpoint.

For example:

..
"donation": {  
  "donation_id": 12345,  
  "donation_amount": 10.0  
},
..`