public GraphTraversal<Vertex, Vertex> addV(final Traversal<?, String> vertexLabelTraversal) {
        if (null == vertexLabelTraversal) throw new IllegalArgumentException("vertexLabelTraversal cannot be null");
        final GraphTraversalSource clone = this.clone();
        clone.gremlinLang.addStep(GraphTraversal.Symbols.addV, vertexLabelTraversal);
        final GraphTraversal.Admin<Vertex, Vertex> traversal = new DefaultGraphTraversal<>(clone);
        return traversal.addStep(new AddVertexStartStep(traversal, vertexLabelTraversal));
    }
Spawns a {@link GraphTraversal} by adding a vertex with the label as determined by a {@link Traversal}. If the
{@code vertexLabelTraversal} is {@code null} then it will default to {@link Vertex#DEFAULT_LABEL}.

@since 3.3.1
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversalSource.java