What is this operator, "??"

This question already has an answer here:

What do two question marks together mean in C#? 16 answers

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Well yeah that looks like an error. The code is looking whether Context.ContentDatabase or Context.Database aren't null , and then continues to use the former, even if it was null .

The code should look like this:

var database = Context.ContentDatabase ?? Context.Database;

if (fieldConfiguration == null && database != null)
{
    Item obj = database.SelectSingleItem(
        string.Format("//*[@@templateid='{0}' and @@key='{1}']", 
            (object) TemplateIDs.TemplateField, (object) fieldName));
}

Where it stores the database in a separate variable using the null-coalescing operator and then operates on that, if it isn't null .

So you should contact the team who provides this library and file a bug with them.

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(Context.ContentDatabase ?? Context.Database) expressions end result is Context.ContentDatabase if Context.ContentDatabase is not null, otherwise it'll be Context.Database . The null-coalesce operator is a step forward to terse null checks.

Docs: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-conditional-operator

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Assuming Context.ContentDatabase and Context.Database are same types. The below code should work.

var contentDatabase = Context.ContentDatabase ?? Context.Database;
if (fieldConfiguration == null && contentDatabase != null)
{
Item obj = contentDatabase.SelectSingleItem(
    string.Format("//*[@@templateid='{0}' and @@key='{1}']", 
        (object) TemplateIDs.TemplateField, (object) fieldName));
}

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