ASP.NET Core - Possible Null Reference Return in Generic Repository

Question

In ASP.NET Core-6 Entity Framework, I am using Generic Repository:

public interface IGenericRepository<T> where T : class
{
    Task<T> GetByIdAsync(object id);
}

public class GenericRepository<T> : IGenericRepository<T> where T : class
{
    private readonly ApplicationDbContext _context;
    internal readonly DbSet<T> _table;

    public GenericRepository(ApplicationDbContext context)
    {
        _context = context;
        _table = context.Set<T>();
    }

    public virtual async Task<T> GetByIdAsync(object id)
    {
        return await _table.FindAsync(id);
    }
}

I got this warning:

'_table' is not null here Possible Null Reference Return in Generic Repository

How do I resolve this?

Thank you

Answer 1

The answer is on another stack exchange site: https://softwareengineering.stackexchange.com/questions/433387/whats-wrong-with-returning-null

Quote

You have enabled the nullable reference types (NRT) feature of C#. This requires you to explicitly specify when a null may be returned. So change the signature to:

public TEntity? Get(Guid id)
{
    // Returns a TEntity on find, null on a miss
    return _entities.Find(id);
}

And the warning will go away.

I'm not using the feature, but expect your code should look like

public virtual async Task<T?> GetByIdAsync(object id)
{
    return await _table.FindAsync(id);
}