[Bug Report]: Resource Group modules for Managedby

[Grant-Rc]

Describe the bug

When updating from the old resources modules, the below code set the managedBy to ''

@description('Optional. The ID of the resource that manages this resource group.')
param managedBy string = ''


resource resourceGroup 'Microsoft.Resources/resourceGroups@2021-04-01' = {
  location: location
  name: name
  tags: tags
  managedBy: managedBy
  properties: {}
}

In the new AVM modules its commented out and so its reverts to $null

resource resourceGroup 'Microsoft.Resources/resourceGroups@2021-04-01' = {
  location: location
  name: name
  tags: tags
  // managedBy: managedBy // removed due to immutable string, only used for managed resource groups
  properties: {}
}

When testing, it will try and update the property but this is not allowed

 "details": [
    {
      "code": "ResourceGroupManagedByMismatch",
      "message": "The managed by property of the resource group cannot be changed from its current value ''."
    }
  ]

To reproduce

Deploy a resource group using the resource deployment of

resource resourceGroup 'Microsoft.Resources/resourceGroups@2021-04-01' = {
  location: location
  name: name
  tags: tags
  managedBy: managedBy
  properties: {}
}

Update the code to comment out the managedBy property

resource resourceGroup 'Microsoft.Resources/resourceGroups@2021-04-01' = {
  location: location
  name: name
  tags: tags
  // managedBy: managedBy // removed due to immutable string, only used for managed resource groups
  properties: {}
}

Code snippet

resource resourceGroup 'Microsoft.Resources/resourceGroups@2021-04-01' = {
  location: location
  name: name
  tags: tags
  managedBy: managedBy
  properties: {}
}

resource resourceGroup 'Microsoft.Resources/resourceGroups@2021-04-01' = {
  location: location
  name: name
  tags: tags
  // managedBy: managedBy // removed due to immutable string, only used for managed resource groups
  properties: {}
}

Relevant log output

"details": [
    {
      "code": "ResourceGroupManagedByMismatch",
      "message": "The managed by property of the resource group cannot be changed from its current value ''."
    }
  ]