public default GraphTraversal<S, Vertex> mergeV() {
        this.asAdmin().getGremlinLang().addStep(Symbols.mergeV);
        final MergeVertexStep<S> step = new MergeVertexStep<>(this.asAdmin(), false);
        return this.asAdmin().addStep(step);
    }
Performs a merge (i.e. upsert) style operation for an {@link Vertex} using the incoming {@code Map} traverser as
an argument. The {@code Map} represents search criteria and will match each of the supplied key/value pairs where
the keys may be {@code String} property values or a value of {@link T}. If a match is not made it will use that
search criteria to create the new {@link Vertex}.

@since 3.6.0
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal.java