code: public String getStringMazeFilled(Collection<Point> points, char symbol) {
          Map<Point, Character> replacements = new HashMap<Point, Character>();
          for (Point p : points) {
              replacements.put(p, symbol);
          }
          return getReplacedMazeString(Collections.singletonList(replacements));
      }
docs: Generates a string representation of this maze, with the indicated points replaced
  with the symbol provided.
  @param points points of the maze.
  @param symbol symbol to be inserted in each point.
  @return the string representation of the maze with the points changed.