Description of problem:
Some entities has optional array parameters that allow nil value. Previously it was possible to send empty list '[]' as value to clear all values, but now according to dLobatog it is not possible because of a new security mechanism in Rails.

Though it affects all the optional parameters, some example entities/parameters are: smart_proxies.locations, location.smart_proxies, organization.smart_proxies, organization.hostgroup_ids.


# Update with empty list
> Making HTTP PUT request to https://sat6.com/katello/api/v2/organizations/39 with options {'verify': False, 'auth': ('admin', 'changeme'), 'headers': {'content-type': 'application/json'}} and data {"organization": {"smart_proxy_ids": []}}.

# Response
> Received HTTP 200 response: 
{
  "name":"XWsKJtxSBN",
  "id":39,
  "smart_proxies":[
    {
      "name":"sat6.com",
      "id":1,
      "url":"https://sat6.com:9090"
    },
    {
      "name":"Oa5c2S",
      "id":11,
      "url":"https://sat6.com:11629"
    }
}

Version-Release number of selected component (if applicable):
Satellite 6.3.0 Snap 6.0, Foreman 1.13.1-1

How reproducible:
Always

Steps to Reproduce:
1. Create entity that has optional array parameters
2. Update that parameter with some value
3. Update that parameter one more time with empty list
4. Check that values from point 2 not changed

Actual results:
When updating with empty list nothing happens, optional parameter has all previous values

Expected results:
All values should be cleared

Additional info: