C# - Null Checking Using C# 7 Discards and the C# 9 Way

Discards.cs

/**********************************************************************************
  Discards (_) do not take up memory. These were introduced in C# 7. 
  
  This code evaluates if variable name has a value then return. Else, throw ANE. 
  Additionally, it uses the null-coalescing operator for null checks.
*/

public static int CountNumberOfSInName(string name)
{
  _ = name ?? throw new ArgumentNullException(nameof(name));

  return name.Count(c => char.ToLower(c).Equals('s'));
}


/**********************************************************************************  
  In the case when deciding to use the value of variable 'name' instead of assigning 
  it to a discard, you can do this: 
*/

private readonly string _name;

public static int CountNumberOfSInName(string name)
{
  _name = name ?? throw new ArgumentNullException(nameof(name));

  return _name.Count(c => char.ToLower(c).Equals('s'));
}

/**********************************************************************************
  The codes above sacrifices readability.

  C# 9 allows the combination of the "is" expression and the "not" logical pattern.
  You can do the following for null checks that preserves readability:
*/

if (name is null) { }
else

// or:

if (name is not null) { }