@Override
    public String toString() {
        final ArrayList args = new ArrayList();
        args.add(serviceName);
        if (!staticParams.get().isEmpty())
            args.add(staticParams);
        if (mapTraversal != null)
            args.add(mapTraversal);
        if (!parameters.isEmpty())
            args.add(parameters);
        return StringFactory.stepString(this, args.toArray());
    }
Reference implementation for service calls via the {@link ServiceRegistry} and {@link Service} APIs. This step
can be used to start a traversal or it can be used mid-traversal with one at a time or barrier execution.

@author Mike Personick (http://github.com/mikepersonick)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/CallStep.java