#vulnerable code 
                              @Override
  public void update(N node) {
    Point2D location = layoutModel.apply(node);
    if (!this.getLayoutArea().contains(location)) {
      log.trace(location + " outside of spatial " + this.getLayoutArea());
      this.setBounds(this.getUnion(this.getLayoutArea(), location));
      this.recalculate(layoutModel.getGraph().nodes());
    }
    SpatialQuadTree<N> locationContainingLeaf = getContainingQuadTreeLeaf(location);
    log.trace("leaf {} contains {}", locationContainingLeaf, location);
    SpatialQuadTree<N> nodeContainingLeaf = getContainingQuadTreeLeaf(node);
    log.trace("leaf {} contains node {}", nodeContainingLeaf, node);
    if (locationContainingLeaf == null) {
      log.error("got null for leaf containing {}", location);
    }
    if (nodeContainingLeaf == null) {
      log.warn("got null for leaf containing {}", node);
    }
    if (!locationContainingLeaf.equals(nodeContainingLeaf)) {
      log.trace("time to recalculate");
      this.recalculate(layoutModel.getGraph().nodes());
    }
    this.insert(node);
  } 
                            #location 19 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              @Override
  public void update(N node) {
    Point2D location = layoutModel.apply(node);
    if (!this.getLayoutArea().contains(location)) {
      log.trace(location + " outside of spatial " + this.getLayoutArea());
      this.setBounds(this.getUnion(this.getLayoutArea(), location));
      this.recalculate(layoutModel.getGraph().nodes());
    }
    SpatialQuadTree<N> locationContainingLeaf = getContainingQuadTreeLeaf(location);
    log.trace("leaf {} contains {}", locationContainingLeaf, location);
    SpatialQuadTree<N> nodeContainingLeaf = getContainingQuadTreeLeaf(node);
    log.trace("leaf {} contains node {}", nodeContainingLeaf, node);
    if (locationContainingLeaf == null) {
      log.error("got null for leaf containing {}", location);
    }
    if (nodeContainingLeaf == null) {
      log.warn("got null for leaf containing {}", node);
    }
    if (locationContainingLeaf != null && !locationContainingLeaf.equals(nodeContainingLeaf)) {
      log.trace("time to recalculate");
      this.recalculate(layoutModel.getGraph().nodes());
    }
    this.insert(node);
  }