code: public static boolean isNullable(Injectee injectee) {
      // HK2's optional
      if (injectee.isOptional()) {
        return true;
      }
      
      // Guice's optional
      AnnotatedElement element = injectee.getParent();
      if (isGuiceOptional(element)) {
        return true;
      }
      
      // Any @Nullable?
      int position = injectee.getPosition();
      
      if (element instanceof Field) {
        return Nullability.allowsNull(((Field)element).getAnnotations());
        
      } else if (element instanceof Method) {
        Annotation annotations[][] = ((Method)element).getParameterAnnotations();
        return Nullability.allowsNull(annotations[position]);
        
      } else if (element instanceof Constructor<?>) {
        Annotation annotations[][] = ((Constructor<?>)element).getParameterAnnotations();
        return Nullability.allowsNull(annotations[position]);
      }
      
      return false;
    }
docs: Returns {@code true} if the given {@link Injectee} can be {@code null}.
  
  @see Optional
  @see Injectee#isOptional()
  @see Nullable
  @see com.google.inject.Inject#optional()
  @see Nullability#allowsNull(Annotation[])