RINUL_MemberIsMissingItemNullabilityAnnotation.md

RINUL: Member is missing item nullability annotation

Cause

The item of a container member or parameter technically can contain null, but it is not indicated whether callers should account for a null value.

Rule description

Resharper performs nullability analysis and issues warnings, such as missing or redundant null checks. Annotating container members and parameters, such as collections, tasks and lazy types, with nullability attributes improves the results of that analysis engine.

How to fix violations

Annotate the target member or parameter with JetBrains.Annotations.ItemCanBeNullAttribute or JetBrains.Annotations.ItemNotNullAttribute.

When to suppress warnings

There is no technical reason to suppress this warning.

Example of a violation

Description

The type C defines container members and parameters that can contain null, which are not annotated.

Code

using System;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace N
{
    public class C
    {
        private readonly List<string> _f = new List<string>();

        public ICollection<string> P => _f.AsReadOnly();

        public Lazy<string> M(Task<string> p)
        {
            _f.Add(p.Result);
            return new Lazy<string>(() => p.Result);
        }
    }
}

Example of how to fix

Description

All container members of the type C that can contain null are now annotated.

Code

using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using JetBrains.Annotations;

namespace N
{
    public class C
    {
        [ItemCanBeNull] private readonly List<string> _f = new List<string>();

        [ItemCanBeNull] public ICollection<string> P => _f.AsReadOnly();

        [ItemNotNull] public Lazy<string> M([ItemNotNull] Task<string> p)
        {
            _f.Add(p.Result);
            return new Lazy<string>(() => p.Result);
        }
    }
}

Related rules

RNUL: Member is missing nullability annotation

XNUL: Suggest to disable reporting on nullable value types