Make key part of the desired state so we can handle new keys

This improved log output and prevents failures when no key has been set:

```
❰tsmith❙~/dev/work/chef(git✱≠macos_userdefaults)❱✔≻ bundle exec chef-apply test.rb
Recipe: (chef-apply cookbook)::(chef-apply recipe)
  * macos_userdefaults[Add String key] action write
    - create Add String key
    -   set key   to "StringKey2"
    -   set value to "/usr/local/tim"
  * macos_userdefaults[Add boolean key] action write (up to date)
  * macos_userdefaults[Add array key] action write (up to date)
❰tsmith❙~/dev/work/chef(git✱≠macos_userdefaults)❱✔≻ bundle exec chef-apply test.rb
Recipe: (chef-apply cookbook)::(chef-apply recipe)
  * macos_userdefaults[Add String key] action write
    - update Add String key
    -   set value to "/usr/local/tim2" (was "/usr/local/tim")
  * macos_userdefaults[Add boolean key] action write (up to date)
  * macos_userdefaults[Add array key] action write (up to date)
```

Signed-off-by: Tim Smith <tsmith@chef.io>

1 files changed, 8 insertions, 4 deletions

diff --git a/lib/chef/resource/macos_userdefaults.rb b/lib/chef/resource/macos_userdefaults.rb
index 15a0f17a39..f45141957a 100644
--- a/lib/chef/resource/macos_userdefaults.rb
+++ b/lib/chef/resource/macos_userdefaults.rb
@@ -75,8 +75,7 @@ class Chef
 
       property :key, String,
         description: "The preference key.",
-        required: true,
-        desired_state: false
+        required: true
 
       property :host, [String, Symbol],
         description: "Set either :current or a hostname to set the user default at the host level.",
@@ -116,9 +115,14 @@ class Chef
 
         plist_data = ::Plist.parse_xml(state.stdout)
 
-        current_value_does_not_exist! unless current_value_does_not_exist!.key?(key)
+        # handle the situation where the key doesn't exist in the domain
+        if plist_data.key?(desired.key)
+          key desired.key
+        else
+          current_value_does_not_exist!
+        end
 
-        value plist_data[key]
+        value plist_data[desired.key]
       end
 
       #