public <S> GraphTraversal<S, S> call(final String service) {
        final GraphTraversalSource clone = this.clone();
        clone.gremlinLang.addStep(GraphTraversal.Symbols.call, service);
        final GraphTraversal.Admin<S, S> traversal = new DefaultGraphTraversal<>(clone);
        return traversal.addStep(new CallStep<>(traversal, true, service));
    }
Spawns a {@link GraphTraversal} starting with values produced by the specified service call with no parameters.

@param service the name of the service call
@since 3.6.0
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversalSource.java