CODEWITHSUNDEEP
c#parameterscompiler-errorsdefaultnullable
Eric Ouellet
Eric Ouellet

Reputation: 11754

Resolve compilation error “CS8601 Possible null reference assignment”

Since C# 8.0, the standard is non nullable variable by default. Ref1

But in case of generics like this one:

    public static T PerfomIO<T>(Func<T> function, T defaultValue = default)
    {
        try
        {
            return function();
        }
        catch (IOException)
        {
        }

        return defaultValue;
    }

How to get rid of the compilation error "CS8601 Possible null reference assignement" that occur when I try to pass "default" ?

I want to support null value here. I do not want to disable the error message. I want to program it the way it should be.

I try to add Nullable in many ways without success. I try [AllowNull] without success

enter image description here

Upvotes: 14

Views: 13543

Answers (2)

Pavel Kovalev
Pavel Kovalev

Reputation: 8126

In Visual Studio 2022 you can add .editorconfig file to suppress those annoying messages (I sure hope you know what you are doing)

In the .sln file:

Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{32FE27E8-3094-4A72-8200-3A2639355EF0}"
        ProjectSection(SolutionItems) = preProject
            .editorconfig = .editorconfig
        EndProjectSection
    EndProject

and .editorconfig file content is:

[*.cs]

# CS8600: Converting null literal or possible null value to non-nullable type.
dotnet_diagnostic.CS8600.severity = none

There is a way to create this file and hook it up suing VS2022 by hovering over the issue:

suppress CS8600

I hope it will help someone 🙂

Upvotes: 0

Eric Ouellet
Eric Ouellet

Reputation: 11754

I found a few tricks although I had no idea why the project was forced to "nullable check" (found and details below). I look in the .csproj, .sln and elsewhere and didn't find any parameter that could force the null check.

I found 2 ways to workaround the problem I had:

  • Solution 1: You can add the next line at the start of your .cs file:

    #nullable disable

  • Solution 2: Change the parameter from default to default! where the ! tells the compiler not to consider the nullable check.

I currently use default!.

Also just as reference, if your project forces null check but you can't find the option in your project or in your solution, then look for this article: Customize your build, perhaps you will find why the null check is forced. (All new since 2019).

Upvotes: 18

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