Installing chef-manage via chef-manage-ctl on SLES 12 not possible

Hello!
I'm trying to install the chef-manage extension via chef-server-ctl on SLES 12 - unfortunately the command fails:

# chef-server-ctl install chef-manage
Starting Chef Client, version 14.3.37
resolving cookbooks for run list: ["private-chef::add_ons_wrapper"]
Synchronizing Cookbooks:
  - private-chef (0.1.1)
  - openssl (8.5.5)
  - runit (4.1.1)
  - enterprise (0.14.1)
  - packagecloud (1.0.0)
  - yum-epel (3.3.0)
Installing Cookbook Gems:
Compiling Cookbooks...

================================================================================
Recipe Compile Error in /var/opt/opscode/local-mode-cache/cookbooks/private-chef/recipes/add_ons_wrapper.rb
================================================================================

NoMethodError
-------------
undefined method `url' for []:Array

Cookbook Trace:
---------------
  /var/opt/opscode/local-mode-cache/cookbooks/private-chef/recipes/add_ons_wrapper.rb:70:in `block in from_file'
  /var/opt/opscode/local-mode-cache/cookbooks/private-chef/recipes/add_ons_wrapper.rb:62:in `each'
  /var/opt/opscode/local-mode-cache/cookbooks/private-chef/recipes/add_ons_wrapper.rb:62:in `from_file'

Relevant File Content:
----------------------
/var/opt/opscode/local-mode-cache/cookbooks/private-chef/recipes/add_ons_wrapper.rb:

 63:      artifact_info = Mixlib::Install.new(
 64:        channel: :stable,
 65:        product_name: pkg.split(/(chef-|opscode-)(.*)/).last,
 66:        product_version: :latest,
 67:        platform_version_compatibility_mode: true
 68:      ).detect_platform.artifact_info
 69:
 70>>     pkg_file = File.join(addon_path, File.basename(artifact_info.url))
 71:
 72:      remote_file pkg_file do
 73:        source artifact_info.url
 74:        checksum artifact_info.sha256
 75:      end
 76:    end
 77:  else
 78:    addon_path = node['private_chef']['addons']['path']
 79:  end

System Info:
------------
chef_version=14.3.37
platform=suse
platform_version=12.4
ruby=ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-linux]
program_name=/opt/opscode/embedded/bin/chef-client
executable=/opt/opscode/embedded/bin/chef-client


Running handlers:
  - #<Class:0x00000000055c18e0>::AddonInstallHandler
Running handlers complete
Chef Client failed. 0 resources updated in 07 seconds
[2019-01-30T15:49:03+01:00] FATAL: Stacktrace dumped to /var/opt/opscode/local-mode-cache/chef-stacktrace.out
[2019-01-30T15:49:03+01:00] FATAL: Stacktrace dumped to /var/opt/opscode/local-mode-cache/chef-stacktrace.out
[2019-01-30T15:49:03+01:00] FATAL: Please provide the contents of the stacktrace.out file if you file a bug report
[2019-01-30T15:49:03+01:00] FATAL: Please provide the contents of the stacktrace.out file if you file a bug report
[2019-01-30T15:49:03+01:00] FATAL: NoMethodError: undefined method `url' for []:Array
[2019-01-30T15:49:03+01:00] FATAL: NoMethodError: undefined method `url' for []:Array

EDIT: In the Chef Manage documentation I saw the following note:

First download the package that is appropriate for the platform, save it to a local path...

On the Chef Support page I saw that SLES 12 is a commercial supported version, but there are no extension packages available for it?

Environment

  • SLES 12 SP4
  • Chef Server 12.18.14 (chef-server-core-12.18.14-1.sles12.x86_64)

Things I've tried / seen
The error is reproducible, it happens every time I try to install the addon.
In another thread I saw that chef-manage can also be downloaded as package: https://downloads.chef.io/manage
I don't see packages for SLES 12 here - so does this mean, that the extension is not available for this platform?

Stacktrace

Generated at 2019-01-30 15:49:03 +0100
NoMethodError: undefined method `url' for []:Array
/var/opt/opscode/local-mode-cache/cookbooks/private-chef/recipes/add_ons_wrapper.rb:70:in `block in from_file'
/var/opt/opscode/local-mode-cache/cookbooks/private-chef/recipes/add_ons_wrapper.rb:62:in `each'
/var/opt/opscode/local-mode-cache/cookbooks/private-chef/recipes/add_ons_wrapper.rb:62:in `from_file'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/mixin/from_file.rb:34:in `instance_eval'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/mixin/from_file.rb:34:in `from_file'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/cookbook_version.rb:199:in `load_recipe'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/run_context.rb:350:in `load_recipe'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/run_context/cookbook_compiler.rb:166:in `block in compile_recipes'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/run_context/cookbook_compiler.rb:163:in `each'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/run_context/cookbook_compiler.rb:163:in `compile_recipes'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/run_context/cookbook_compiler.rb:79:in `compile'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/run_context.rb:199:in `load'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/policy_builder/expand_node_object.rb:97:in `setup_run_context'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/client.rb:515:in `setup_run_context'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/client.rb:281:in `run'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/application.rb:303:in `run_with_graceful_exit_option'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/application.rb:279:in `block in run_chef_client'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/local_mode.rb:44:in `with_server_connectivity'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/application.rb:261:in `run_chef_client'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/application/client.rb:440:in `run_application'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/lib/chef/application.rb:66:in `run'
/opt/opscode/embedded/lib/ruby/gems/2.5.0/gems/chef-14.3.37/bin/chef-client:25:in `<top (required)>'
/opt/opscode/embedded/bin/chef-client:23:in `load'
/opt/opscode/embedded/bin/chef-client:23:in `<main>'