Checking for Null in Constructor

To the compiler, null is a legitimate constructor argument.

Your class might be able to handle a null value for myObject. But if it can't - if your class will break when myObject is null - then checking in the constructor allows you to fail fast.

Passing a null object is perfectly legal in many cases - for this class the implementor wants to ensure that you cannot create an instance of the class w/o passing a valid Object instance though, so there have to be no checks later on - it's a good practice to ensure this as early as possible, which would be in the constructor.

if you under 4.0 you can do the following:

 public ctor(IEnjection ninjaWeapon) 
 {
     Contract.Requires<ArgumentNullException>(ninjaWeapon != null);
     this.deadlyWeaponary.Add(ninjaWeapon);
 }

if you under an older version, reference the Microsoft.Contract to do the same thing.