EitherAsync returns Null for Left value when used in Linq query

[naveen-negi]

When I'm trying to chain EitherAsync, final value is always null in case of left. I have a sample below. Function HappyPath works as expected, however, EarlyExitOnFailure return null instead of first that it encounters in the chain.

public static class TestEitherAsync
{
    public static EitherAsync<A, B> EitherAOrBLeft()
    {
        return new A();
    }

    public static EitherAsync<A, B> EitherAOrBRight()
    {
        return new B();
    }

    public static EitherAsync<C, D> EitherCOrDLeft()
    {
        return new C();
    }

    public static EitherAsync<C, D> EitherCOrDRight()
    {
        return new D();
    }

    public static async Task<E> EarlyExitOnFailure()
    {
        var result = await (from b in EitherAOrBLeft()
            from d in EitherCOrDLeft()
            select new E(b, d)).FirstOrDefaultAsync();
        return result!;
    }

    public static async Task<E> HappyPath()
    {
        var result = await (from b in EitherAOrBRight()
            from d in EitherCOrDRight()
            select new E(b, d)).FirstOrDefaultAsync();
        return result!;
    }
}

public record A();
public record B();
public record C();

public record D();

public record E(B First, D Second);

[louthy]

It’s hardly surprising, calling FirstOrDefault for empty sequences returns null. It’s a LINQ operator that I don’t control.

Use Match to work with the Left or Right values.