#vulnerable code 
                              protected V getClosest(
      SpatialQuadTree<V> spatial, LayoutModel<V, Point2D> layoutModel, double x, double y) {
    SpatialQuadTree<V> leaf = spatial.getContainingQuadTreeLeaf(x, y);
    double diameter = leaf.getLayoutArea().getWidth();
    double radius = diameter / 2;
    double minDistance = Double.MAX_VALUE;

    V closest = null;
    Ellipse2D target = new Ellipse2D.Double(x - radius, y - radius, diameter, diameter);
    Collection<V> nodes = spatial.getVisibleNodes(target);
    if (log.isTraceEnabled()) {
      log.trace("instead of checking all nodes: {}", getFilteredVertices());
      log.trace("out of these candidates: {}...", nodes);
    }
    for (V node : nodes) {
      Shape shape = vv.getRenderContext().getVertexShapeTransformer().apply(node);
      // get the vertex location
      Point2D p = layoutModel.apply(node);
      if (p == null) {
        continue;
      }
      // transform the vertex location to screen coords
      p = vv.getRenderContext().getMultiLayerTransformer().transform(Layer.LAYOUT, p);

      double ox = x - p.getX();
      double oy = y - p.getY();

      if (shape.contains(ox, oy)) {

        if (style == Style.LOWEST) {
          // return the first match
          return node;
        } else if (style == Style.HIGHEST) {
          // will return the last match
          closest = node;
        } else {

          // return the vertex closest to the
          // center of a vertex shape
          Rectangle2D bounds = shape.getBounds2D();
          double dx = bounds.getCenterX() - ox;
          double dy = bounds.getCenterY() - oy;
          double dist = dx * dx + dy * dy;
          if (dist < minDistance) {
            minDistance = dist;
            closest = node;
          }
        }
      }
    }
    if (log.isTraceEnabled()) {
      log.trace("picked {} with spatial quadtree", closest);
    }
    return closest;
  } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              protected V getClosest(
      SpatialQuadTree<V> spatial, LayoutModel<V, Point2D> layoutModel, double x, double y) {

    // move the x,y to layout coordinates
    Point2D pickPointInView = new Point2D.Double(x, y);
    Point2D pickPointInLayout =
        vv.getRenderContext()
            .getMultiLayerTransformer()
            .inverseTransform(Layer.LAYOUT, pickPointInView);
    if (log.isTraceEnabled()) {
      log.trace("pickPoint in view {} layout {}", pickPointInView, pickPointInLayout);
    }

    double lx = pickPointInLayout.getX();
    double ly = pickPointInLayout.getY();

    SpatialQuadTree<V> leaf = spatial.getContainingQuadTreeLeaf(lx, ly);
    if (log.isTraceEnabled()) {
      log.trace("leaf for {},{} is {}", lx, ly, leaf);
    }
    if (leaf == null) return null;
    double diameter = leaf.getLayoutArea().getWidth();
    double radius = diameter / 2;
    double minDistance = Double.MAX_VALUE;

    V closest = null;
    Ellipse2D target = new Ellipse2D.Double(lx - radius, ly - radius, diameter, diameter);
    if (log.isTraceEnabled()) {
      log.trace("target is {}", target);
    }
    Collection<V> nodes = spatial.getVisibleNodes(target);
    if (log.isTraceEnabled()) {
      log.trace("instead of checking all nodes: {}", getFilteredVertices());
      log.trace("out of these candidates: {}...", nodes);
    }
    for (V node : nodes) {
      Shape shape = vv.getRenderContext().getVertexShapeTransformer().apply(node);
      // get the vertex location
      Point2D p = layoutModel.apply(node);
      if (p == null) {
        continue;
      }
      // transform the vertex location to screen coords
      p = vv.getRenderContext().getMultiLayerTransformer().transform(Layer.LAYOUT, p);

      double ox = x - p.getX();
      double oy = y - p.getY();

      if (shape.contains(ox, oy)) {

        if (style == Style.LOWEST) {
          // return the first match
          return node;
        } else if (style == Style.HIGHEST) {
          // will return the last match
          closest = node;
        } else {

          // return the vertex closest to the
          // center of a vertex shape
          Rectangle2D bounds = shape.getBounds2D();
          double dx = bounds.getCenterX() - ox;
          double dy = bounds.getCenterY() - oy;
          double dist = dx * dx + dy * dy;
          if (dist < minDistance) {
            minDistance = dist;
            closest = node;
          }
        }
      }
    }
    if (log.isTraceEnabled()) {
      log.trace("picked {} with spatial quadtree", closest);
    }
    return closest;
  }