code: public void check_in(double[] p) {
          if (p != null) {
              L.add(p);
          } else {
              System.out.println("Miniball.check_in WARNING: Skipping null point");
          }
      }
docs: Adds a point to the list.<br>
  Skip action on null parameter.<br>
  @param p The object to be added to the list