code: public boolean endLink(final Object endVertex, final MouseEvent mouseEvent) {
          logger.debug("endLink({})", endVertex);
          boolean result = false;
          if (_startVertex != null && endVertex != null) {
              if (mouseEvent.getButton() == MouseEvent.BUTTON1) {
                  final boolean created = createLink(_startVertex, endVertex, mouseEvent);
                  if (created && _graphContext.getVisualizationViewer().isVisible()) {
                      _graphContext.getJobGraph().refresh();
                  }
                  result = true;
              }
          }
          stopDrawing();
          return result;
      }
docs: If startVertex is non-null this method will attempt to end the
  link-painting at the given endVertex
  
  @return true if a link drawing was ended or false if it wasn't started