JetBrains Rider中的自定义null断言

Question

I have a custom extension method for checking Guid? values:

public static bool IsNullOrDefault(this Guid? guid)
{
    return !guid.HasValue || guid.value == Guid.Empty;
}

When I use the method in my code, I would expect that Rider will consider this method in possible System.InvalidOperationException assertions. But it does not.

public void Foo(Guid? guid)
{
    if (guid.IsNullOrDefault())
    {
        throw new Exception();
    }

    var x = guid.Value;
            ^ There is still a yellow squiggle here, saying Possible System.InvalidOperationException
    ...
}

I have tried creating my own Null Checking pattern by overwriting the Custom (statement) pattern:

if ($EXPR$.IsNullOrDefault()) throw new System.ArgumentNullException($NAME$);

But that does not work either. How can I configure Rider to consider my custom method an equivalent to guid.HasValue or guid != null ?

Answer 1

I'm not sure Rider is intelligent enough to recognize that you already checked this. I think what you can do instead, is use the ?. notation to check for null

var x = guid?.Value;

This check if guid is null before the .value is evaluated, and just return null if that's the case.

Then you can put the check afterward instead, so it ends up like

var x guid?.value;
if(x is null)
    Throw new Exception();

Or you can return a default value instead of throwing an exception, your call.

Let me know how it works!