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"]

Commencez par examiner les schémas JSON des ressources DSC listées ainsi que la propriété canonique _inDesiredState, en utilisant la liste des ressources et des propriétés de l’issue comme périmètre. Vérifiez quelles propriétés acceptent réellement null plutôt que d’être simplement facultatives, puis validez les schémas obtenus par rapport à la sémantique documentée de JSON Schema et aux attentes de l’autocomplétion de Bicep. Le travail est terminé lorsque les types null injustifiés sont supprimés tout en conservant les valeurs nullable légitimes.