Satellite 6.2: `hammer bootdisk host` or host image download via UI fails with ERF42-2759 [Foreman::Exception]

Issue

• hammer bootdisk host fails when the default gateway or DNS is not set in subnet definition
• Downloading a "host image" via UI for a host in a subnet without default gateway or DNS servers fails
• Although Gateway address and "DNS Servers" are marked "Optional" in UI, if not set, boot disk creation via hammer or download via UI fails
• Why do I get the following error message when trying to create a host bootdisk via hammer :

Failed to download host disk image:
  ERF42-2759 [Foreman::Exception]: Subnet (static-no-gw-vlan105.example.com (172.24.105.0/24)) has no gateway defined

or 

Error: Failed to render boot disk template: ERF42-2759 [Foreman::Exception]: Subnet (static-no-gw-vlan105.example.com (172.24.105.0/24)) has no gateway defined

• Why do I get the following error message when trying to download a "host image" via UI:

Failed to download host disk image:
  ERF42-1701 [Foreman::Exception]: Subnet (static-no-gw-vlan105.example.com (172.24.105.0/24)) has no primary DNS server defined


or

Error: Failed to render boot disk template: ERF42-1701 [Foreman::Exception]: Subnet (static-no-gw-vlan105.example.com (172.24.105.0/24)) has no primary DNS server defined