code: public final void addConstructor(final SgConstructor constructor) {
          if (constructor == null) {
              throw new IllegalArgumentException("The argument 'constructor' cannot be null!");
          }
          if (constructor.getOwner() != this) {
              throw new IllegalArgumentException(
                      "The owner of 'constructor' is different from 'this'!");
          }
          if (!constructors.contains(constructor)) {
              constructors.add(constructor);
          }
      }
docs: Adds a constructor to the class. Does nothing if the constructor is
  already in the list of constructors. You will never need to use this
  method in your code! A constructor is added automatically to the owning
  class when it's constructed!
  
  @param constructor
  Constructor to add - Cannot be null.