Not able to add existing storage account to enable diagnostic logs during azure VM creation using farmer

The Farmer library has builder for Virtual machine creation, though it has support for parameter "diagnostics_support_external" which enables the boot diagnostics with existing created storage account.

let storageAccount =  LinkedResource.Unmanaged resourceId
vm {
  diagnostics_support_external storageAccount
}

But it generates the incorrect arm template. Currently it generates the arm template with following property attached to it.

"properties": {
        "diagnosticsProfile": {
          "bootDiagnostics": {
            "enabled": true,
            "storageUri": "[reference('sa0ce3c1e410a5ec454941').primaryEndpoints.blob]"
          }
        },

The above generated templates fail to create resources as Azure complains with following error

{
  "code": "InvalidTemplate",
  "message": "Deployment template validation failed: 'The template reference 'sa0ce3c1e410a5ec454941' is not valid: could not find template resource or resource copy with this name. Please see https://aka.ms/arm-template-expressions/#reference for usage details.'."
}

The correct template should look like this, as after this modification Azure is able to resolve the Storage Account resource.

"diagnosticsProfile": {
          "bootDiagnostics": {
            "enabled": true,
            "storageUri": "[reference(concat('Microsoft.Storage/storageAccounts/', 'sa0ce3c1e410a5ec454941'),'2015-06-15').primaryEndpoints.blob]"
          }
        },

Can anyone help.