Error when deploying customers.gitlab.com

```
  * cookbook_file[/var/chef/handlers/prometheus_handler.rb] action create[2018-11-05T18:03:43+00:00] INFO: Processing cookbook_file[/var/chef/handlers/prometheus_handler.rb] action create (gitlab-exporters::chef_client line 20)
 (up to date)
  * chef_handler[PrometheusHandler] action enable[2018-11-05T18:03:43+00:00] INFO: Processing chef_handler[PrometheusHandler] action enable (gitlab-exporters::chef_client line 27)
[2018-11-05T18:03:43+00:00] INFO: Enabling PrometheusHandler as a report handler.
[2018-11-05T18:03:43+00:00] INFO: Enabling PrometheusHandler as a exception handler.
 (up to date)
[2018-11-05T18:03:43+00:00] WARN: This cookbook is being re-written to use resources, not recipes and will only be Chef 13.8+ compatible. Please version pin to 6.1.1 to prevent the breaking changes from taking effect. See https://github.com/sous-chefs/postgresql/issues/512 for details
[2018-11-05T18:03:43+00:00] WARN: This cookbook is being re-written to use resources, not recipes and will only be Chef 13.8+ compatible. Please version pin to 6.1.1 to prevent the breaking changes from taking effect. See https://github.com/sous-chefs/postgresql/issues/512 for details
[2018-11-05T18:03:43+00:00] WARN: This cookbook is being re-written to use resources, not recipes and will only be Chef 13.8+ compatible. Please version pin to 6.1.1 to prevent the breaking changes from taking effect. See https://github.com/sous-chefs/postgresql/issues/512 for details
  
  ================================================================================
  Recipe Compile Error in /var/chef/cache/cookbooks/cookbook-customers-gitlab-com/recipes/default.rb
  ================================================================================
  
  NoMethodError
  -------------
  undefined method `[]' for nil:NilClass
  
  Cookbook Trace:
  ---------------
    /var/chef/cache/cookbooks/postgresql/recipes/apt_pgdg_postgresql.rb:6:in `block in from_file'
    /var/chef/cache/cookbooks/postgresql/recipes/apt_pgdg_postgresql.rb:4:in `from_file'
    /var/chef/cache/cookbooks/postgresql/recipes/client.rb:10:in `from_file'
    /var/chef/cache/cookbooks/postgresql/recipes/server.rb:23:in `from_file'
    /var/chef/cache/cookbooks/cookbook-customers-gitlab-com/recipes/database.rb:9:in `from_file'
    /var/chef/cache/cookbooks/cookbook-customers-gitlab-com/recipes/default.rb:11:in `from_file'
  
  Relevant File Content:
  ----------------------
  /var/chef/cache/cookbooks/postgresql/recipes/apt_pgdg_postgresql.rb:
  
    1:  Chef::Log.warn 'This cookbook is being re-written to use resources, not recipes and will only be Chef 13.8+ compatible. Please version pin to 6.1.1 to prevent the breaking changes from taking effect. See https://github.com/sous-chefs/postgresql/issues/512 for details'
    2:  
    3:  # frozen_string_literal: true
    4:  apt_repository 'apt.postgresql.org' do
    5:    uri 'http://apt.postgresql.org/pub/repos/apt'
    6>>   distribution "#{node['postgresql']['pgdg']['release_apt_codename']}-pgdg"
    7:    components ['main', node['postgresql']['version']]
    8:    key 'https://www.postgresql.org/media/keys/ACCC4CF8.asc'
    9:    action :add
   10:  end
   11:  
  
  Platform:
  ---------
  x86_64-linux
  
  
  Running handlers:
[2018-11-05T18:03:43+00:00] ERROR: Running exception handlers
    - PrometheusHandler
  Running handlers complete
[2018-11-05T18:03:43+00:00] ERROR: Exception handlers complete
  Chef Client failed. 0 resources updated in 20 seconds
[2018-11-05T18:03:43+00:00] FATAL: Stacktrace dumped to /var/chef/cache/chef-stacktrace.out
[2018-11-05T18:03:43+00:00] FATAL: Please provide the contents of the stacktrace.out file if you file a bug report
[2018-11-05T18:03:43+00:00] ERROR: undefined method `[]' for nil:NilClass
[2018-11-05T18:03:43+00:00] FATAL: Chef::Exceptions::ChildConvergeError: Chef run process exited unsuccessfully (exit code 1)
```

Story points: 1.0