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

@since 3.1.0-incubating
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversalSource.java