private static void checkVertex(MetadataGraphVertex v) throws MetadataResolutionException {
        if (v == null) {
            throw new MetadataResolutionException("null vertex");
        }
        if (v.getMd() == null) {
            throw new MetadataResolutionException("vertex without metadata");
        }
    }

        return classpath;
    }

    // -------------------------------------------------------------------------------------------
    public MetadataTreeNode getClasspathAsTree() throws MetadataResolutionException {
        if (classpath == null || classpath.isEmpty()) {
            return null;
        }

        MetadataTreeNode tree = null;
        MetadataTreeNode parent = null;

                    res.addEdge(sourceV, newV, edge);
                }
            }
            return findLinkedSubgraph(res);
        } catch (MetadataResolutionException e) {
            throw new GraphConflictResolutionException(e);
        }
    }

    // -------------------------------------------------------------------------------------