code: @Override
      public void addNearestNeighbours(@Nonnull Element element) {
          if (element == null) {
              throw new IllegalArgumentException("An element must be specified.");
          }
  
          if (element instanceof Person || element instanceof SoftwareSystem) {
              super.addNearestNeighbours(element, Person.class);
              super.addNearestNeighbours(element, SoftwareSystem.class);
          } else {
              throw new IllegalArgumentException("A person or software system must be specified.");
          }
      }
docs: Adds all software systems and people that are directly connected to the specified element.
  
  @param element   an Element