Are these checking on the pass-in parameters necessary?
<p>I have listed five different scenarios that I think the null-checking is necessary in the product code. Although, most of the reference books I have checked do NOT make such checkings. It is reasonable to ignore those checking while the original reference tries to deliver the other important ideas. Here, I summarize all my concerns as follows and please correct me if there are errors.</p>

<pre><code>class Student
{
    public string Name { get; set; }

    public Student(string name)
    {
        Name = name;
    }

    public Student() { }

    public override string ToString()
    {
        return string.Format("Name: {0}", Name);
    }
}

class StudentNameComparer : IComparer&lt;Student&gt;
{
    public int Compare(Student x, Student y)
    {
        if ( (x == null) || (y == null) ) // &lt;C1&gt; Should we check there?
            throw new ArugmentNullException("bla bla");

        return x.Name.CompareTo(y.Name);
    }
}
////////////////////////////////////////////////////
List&lt;Student&gt; students = new List&lt;Student&gt; {
    new Student("s1"),
    new Student("s4"),
    new Student("s3"),
    new Student("s2")
};
students.Sort(delegate(Student x, Student y) 
    { 
        if ( (x == null) || (y == null) ) // &lt;C2&gt; Should we check there?
            throw new ArugmentNullException("bla bla");

        return x.Name.CompareTo(y.Name);    
    });

////////////////////////////////////////////////////    
List&lt;Student&gt; students = new List&lt;Student&gt; {
    new Student("s1"),
    new Student("s4"),
    new Student("s3"),
    new Student("s2")
};
students.Sort( (x, y) =&gt; 
    {
        if ( (x == null) || (y == null) ) // &lt;C3-1&gt; Should we check there?
            throw new ArugmentNullException("bla bla");

        return x.Name.CompareTo(y.Name);    
    });
Or
students.Sort( (Student x, Student y) =&gt; 
    {
        if ( (x == null) || (y == null) ) // &lt;C3-2&gt; Should we check there?
            throw new ArugmentNullException("bla bla");

        return x.Name.CompareTo(y.Name);    
    });
////////////////////////////////////////////////////    
List&lt;Student&gt; students = new List&lt;Student&gt; {
    new Student("s1"),
    new Student("s4"),
    new Student("s3"),
    new Student("s2")
};
foreach (Student std in students.OrderBy(p =&gt; 
    { 
        if (p == null) // &lt;C4&gt; Should we check there?
        {
            throw new ArgumentNullException("...");
        }
        return p.Name;                
    }))
{
    Console.WriteLine(std);
}
</code></pre>
