@Override
    public MemoryComputeKey<E> getMemoryComputeKey() {
        return MemoryComputeKey.of(this.getId(), this.getBiOperator(), false, true);
    }
If the {@code seedSupplier} is {@code null} then this method is called.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/ReducingBarrierStep.java