Unexpected gc alloc behavior in linkedList.find()

As we all know that if we compare a value type variable with null,it will cause GC alloc cause of boxing:

{
    public class TestGeneric<T>{

        public static bool TestGC(T key)
        {
            return key == null;
        }
    }
    TestGeneric<int>.TestGC(10);
}

However, I found that the Find(T value) method of LinkedList(System.Collections.Generic) used same code like

public LinkedListNode<T> Find(T value)
{
    if (value != null)
    {
        //....
    }
}

But the calling like

//LinkedList<int> list;
list.Find(10);

will NOT cause any GC alloc.

I am really confused about that. Any body got an idea? Please Help.Thanks a lot.

====================

Test enviroment: Unity 2018, Unity Profiler(Deep Profile Enable) .Net Version:4.0

Here is my test code.

public class TestGeneric<T> {

    public static bool TestGC(T key)
    {
        return key == null;
    }
}

public class LinkedListTest : MonoBehaviour
{
    LinkedList<int> list = new LinkedList<int>();
    void Start()
    {
        for (int i = 0; i < 10; ++i)
        {
            list.AddLast(i);
        }
    }
    void Update()
    {
        for (int i = 0; i < 10; ++i)
        {
            TestGeneric<int>.TestGC(10);
        }
        for (int i = 0; i < 10; ++i)
        {
            list.Find(100);
        }
    }
}

The unity profiler shows

TestGC method caused 200Byte GC Alloc per frame.

list.Find method caused 0Byte GC Alloc per frame.