throwing an exception if an object is null

As of .NET 6, you can use the ArgumentNullException.ThrowIfNull() static method:

void HelloWorld(string argumentOne)
{
    ArgumentNullException.ThrowIfNull(argumentOne);
    Console.WriteLine($"Hello {argumentOne}");
}

Yes, as of C# 7 you can use Throw Expressions

var firstName = name ?? throw new ArgumentNullException("Mandatory parameter", nameof(name));

Source

There is no similar fashion syntax in C# 6.

However, if you want you can simplify null check by using an extension methods...

 public static void ThrowIfNull(this object obj)
    {
       if (obj == null)
            throw new Exception();
    }

usage

foo.ThrowIfNull();

Or improvement it to display null object name.

 public static void ThrowIfNull(this object obj, string objName)
 {
    if (obj == null)
         throw new Exception(string.Format("{0} is null.", objName));
 }

foo.ThrowIfNull("foo");