var foo = new Foo();
var bar = new Bar();
foo.ToString();
bar.ToString();

internal struct Foo
{
    public override string ToString() => "I'm Foo!";
}

internal struct Bar
{
}

entrypoint
.locals init (
       [0] valuetype Foo V_0,
       [1] valuetype Bar V_1
)

IL_0000: ldloca.s V_0
IL_0002: initobj Foo
IL_0008: ldloca.s V_1
IL_000a: initobj Bar
IL_0010: ldloca.s V_0
IL_0012: constrained. Foo
IL_0018: callvirt instance string [System.Runtime]System.Object::ToString()
IL_001d: pop
IL_001e: ldloca.s V_1
IL_0020: constrained. Bar
IL_0026: callvirt instance string [System.Runtime]System.Object::ToString()
IL_002b: pop
IL_002c: ret

var foo = new Foo();

for (var j = 0; j < 10; j++)
{
    for (var i = 0; i < 100500000; i++)
    {
        foo.ToString();
    }

    Console.WriteLine(GC.GetTotalAllocatedBytes());
}

internal struct Foo
{
    public override string ToString() => null;
}

    // public override string ToString() => null;

IL_0012: constrained. Foo
IL_0018: callvirt instance string [System.Runtime]System.Object::ToString()

public override int GetHashCode() => 0;

public class EntityWithId<T>
{
   public T Id { get;set; }
}

public static bool IsNull(this object obj)
{
    return obj == null;
}