docs: synchronized public Reservoir merge( Reservoir other ) {
          Reservoir result = new Reservoir(this.reservoirSize);
          for(SampleItem item : this.minHeap ) {
              result.add(item);
          }
          if( other != null ) {
              for(SampleItem item : other.minHeap ) {
                  result.add(item);
              }
          }
          return( result );
      }