docs: public void addLast(final T node) {
          if ( this.firstNode == null ) {
              this.firstNode = node;
              this.lastNode = node;
          } else {
              T currentLast = this.lastNode;
              currentLast.setNext( node );
              node.setPrevious( currentLast );
              this.lastNode = node;            
          }
          
          this.size++;
      }