Description of problem:

    Trying to make API call:
    PUT /api/v2/hosts/bulk/add_subscriptions
     
    With data:
     
    {"organization_id": 15, "included": {"ids": [13, 14]}, "excluded": {}, "subscriptions": [{"id": 59, "quantity": 1}]}
     
    I get error:
    NoMethodError: undefined method `candlepin_consumer' for nil:NilClass



Version-Release number of selected component (if applicable):
~]# rpm -q satellite
satellite-6.8.0-0.6.beta.el7sat.noarch
~]# rpm -q candlepin
candlepin-3.1.14-1.el7sat.noarch

How reproducible:
Every time


Steps to Reproduce:
1. Create host collection with two content host entries
2. Create a custom product
3. Attempt to attach subscription for custom product using API path: PUT /api/v2/hosts/bulk/add_subscriptions

Actual results:
Internal Service Error (ISE)
NoMethodError: undefined method `candlepin_consumer' for nil:NilClass

Expected results:
useful error message


Additional info:
https://theforeman.org/plugins/katello/3.15/api/apidoc/v2/hosts_bulk_actions/add_subscriptions.html