Resource and Canonical Properties use of null

Prerequisites

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Summary

There are built-in resources and canonical properties (_inDesiredState) that use null in addition to actual type of the property. Null should NOT be a valid type unless the property actually accepts null as a valid use case. By allowing null it can confuse users when we have auto-complete in BICEP and weakens the strongly validated schema.

JSON schema null and undefined properties are different.

https://json-schema.org/understanding-json-schema/reference/null

Excerpt:

It's important to remember that in JSON, null isn't equivalent to something being absent. See Required Properties for an example.

The mechanism to indicate a property is required or optional is by the use of the required property.

I understand that we're using nullable types so we can return only the properties that are actually defined instead of empty strings or false bools but it is not best practice.

Resources with Nullable Properties:

1. Microsoft.DSC.Debug/Echo
   showSecrets: type: ["boolean", "null"]

2. Microsoft.DSC.Transitional/PowerShellScript
   getScript: type: ["string", "null"]
   setScript: type: ["string", "null"]
   testScript: type: ["string", "null"]
   input: type: ["string", "boolean", "integer", "object", "array", "null"]
   output: type: ["array", "null"]
   _inDesiredState: type: ["boolean", "null"]

3. Microsoft.DSC.Transitional/WindowsPowerShellScript
   getScript: type: ["string", "null"]
   setScript: type: ["string", "null"]
   testScript: type: ["string", "null"]
   input: type: ["string", "boolean", "integer", "object", "array", "null"]
   output: type: ["array", "null"]
   _inDesiredState: type: ["boolean", "null"]

4. Microsoft.OpenSSH.SSHD/Windows
   shell: type: ["string", "null"]
   cmdOption: type: ["string", "null"]
   escapeArguments: type: ["boolean", "null"]

5. Microsoft.Windows/RebootPending
   reasons: type: ["array", "null"]
   The entire object itself: type: ["object", "null"]

6. Microsoft.Windows/Registry
   _metadata: anyOf: [{"$ref": "#/$defs/Metadata"}, {"type": "null"}]
   valueName: type: ["string", "null"]
   valueData: anyOf: [{"$ref": "#/$defs/RegistryValueData"}, {"type": "null"}]
   _exist: type: ["boolean", "null"]

まず、一覧に記載された DSC リソースの JSON スキーマと、正規の _inDesiredState プロパティを確認します。対象範囲は issue のリソースおよびプロパティ一覧とします。各プロパティが実際に null を受け入れるのか、それとも単に省略可能なのかを確認し、そのうえで、結果のスキーマを文書化された JSON Schema のセマンティクスおよび Bicep のオートコンプリートの期待値に照らして検証します。不当な null 型を削除しつつ、正当な nullable 値を維持できれば完了です。