DbSet<TEntity>.FindAsync() returns ValueTask<TEntity> instead of ValueTask<TEntity?>

[prefetcher-gl]

Version Used:
VS 2019 Version 16.5.1
.NET Core 3.1.3

Also tested on:
VS 2019 16.6.0 Preview 2.0
.NET 5.0.0-preview.1

Steps to Reproduce:

public async Task<string> GetString()
{
    DbSet<string> dbSetStrings = null!;
    string? canBeNull = await dbSetStrings.FindAsync();
    return canBeNull;
}

Actual Behavior:
VS popup tip on return canBeNull says that "canBeNull is not null here". MS Docs tells "If no entity is found, then null is returned", doc comments in metadata of DbSet tells the same.
Change DbSet<string> dbSetStrings to DbSet<string?> dbSetStrings and tip says "may be null here" on return canBeNull.

Expected Behavior:
DbSet<TEntity>.FindAsync() may return ValueTask with null, so the return type must be ValueTask<TEntity?>.

BTW, the method return type from metadata is ValueTask<TEntity>, but it shows Task<TEntity> in the Docs.

[YairHalberstadt]

Most of the BCL has not yet been annotated. Either way this is an issue for dotnet/runtime

[prefetcher-gl]

Oh, yes... Please transfer this issue to dotnet/efcore (or where it should be).

[ajcvickers]

Duplicate of #19007