Resource and Canonical Properties use of null

Prerequisites

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• Make sure you are able to repro it on the latest version
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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"]

Comienza revisando los esquemas JSON de los recursos DSC enumerados y la propiedad canónica _inDesiredState, utilizando como alcance la lista de recursos y propiedades del issue. Comprueba qué propiedades aceptan realmente null frente a las que simplemente son opcionales y, a continuación, valida los esquemas resultantes con respecto a la semántica documentada de JSON Schema y a las expectativas del autocompletado de Bicep. El trabajo estará terminado cuando se eliminen los tipos null injustificados y se conserven los valores nullable legítimos.