CheckedOutByUser.UserPrincipalName raises ServerObjectNullReferenceException

Target SharePoint environment

SharePoint Online

What SharePoint development model, framework, SDK or API is this about?

SharePoint CSOM

Developer environment

Windows

What browser(s) / client(s) have you tested

• 💥 Internet Explorer
• 💥 Microsoft Edge
• 💥 Google Chrome
• 💥 FireFox
• 💥 Safari
• mobile (iOS/iPadOS)
• mobile (Android)
• not applicable
• other (enter in the "Additional environment details" area below)

Additional environment details

.NET 6
Microsoft.SharePointOnline.CSOM 16.1.22810.12000

Describe the bug / error

We try to minimize the number of calls to SharePoint online due to throttling issues.

After a checkout we need to refresh the SPFile object to reflect the newest changes.

But after the refresh the SPFile.CheckedOutByUser.ServerObjectIsNull is still true, while the file is checked out.

Steps to reproduce

Code to reproduce issue.

// Create a context per thread as ClientContext is not thread safe
var clientContext = CreateClientContext(instance, client, sharePointAccessToken);

// Make sure this file exists and is not checked out already
var fileUrl = @"https://idbdevelopment.sharepoint.com/Shared%20Documents/document.docx";

var spfile = clientContext.Web.GetFileByUrl(fileUrl);

clientContext.Load(spfile, f => f.Exists, f => f.CheckOutType, f => f.CheckedOutByUser.UserPrincipalName);
clientContext.ExecuteQuery();

Console.WriteLine(spfile.CheckOutType.ToString()); // Should output 'None'
Console.WriteLine(spfile.CheckedOutByUser.ServerObjectIsNull); // Should output TRUE

spfile.CheckOut();

Console.WriteLine(spfile.CheckOutType.ToString()); // Should still output 'None' because the call is not executed yet
Console.WriteLine(spfile.CheckedOutByUser.ServerObjectIsNull); // Should still output TRUE because the call is not executed yet

clientContext.ExecuteQuery();

// Now load CheckOutType and CheckedOutByUser.UserPrincipalName again
clientContext.Load(spfile, f => f.Exists, f => f.CheckOutType, f => f.CheckedOutByUser.UserPrincipalName);
clientContext.ExecuteQuery();
Console.WriteLine(spfile.CheckOutType.ToString()); // None is changed to output 'Online'

// ISSUE:
// The ServerObjectIsNull is still true, while the JSON response from the SharePoint online API contains a checkout user object
Console.WriteLine(spfile.CheckedOutByUser.ServerObjectIsNull); // Should output FALSE
try
{
	// Should output user principal name, but fails with exception:
	// Microsoft.SharePoint.Client.ServerObjectNullReferenceException: 'Object reference not set to an instance of an object on server. The object is associated with identity 
	Console.WriteLine(spfile.CheckedOutByUser.UserPrincipalName); 
}
catch(Exception ex)
{
	Console.WriteLine(ex.ToString());

	// Workaround is to create a new spfile object, but this is an extra unneeded call (increasing throttling issues)
	spfile = clientContext.Web.GetFileByUrl(fileUrl);

	clientContext.Load(spfile, f => f.Exists, f => f.CheckOutType, f => f.CheckedOutByUser.UserPrincipalName);
	clientContext.ExecuteQuery();
}

Console.WriteLine(spfile.CheckedOutByUser.ServerObjectIsNull); // Should still output FALSE
Console.WriteLine(spfile.CheckedOutByUser.UserPrincipalName); // Should output user principal name

Expected behavior

After lines

// Now load CheckOutType and CheckedOutByUser.UserPrincipalName again
clientContext.Load(spfile, f => f.Exists, f => f.CheckOutType, f => f.CheckedOutByUser.UserPrincipalName);
clientContext.ExecuteQuery();

The SPFile.CheckedOutByUser.UserPrincipalName should contain the name of the user that has checked out the file.