class SingleShardRequest<Request extends SingleShardRequest<Request>> extends TransportRequest implements IndicesRequest {

    public static final IndicesOptions INDICES_OPTIONS = IndicesOptions.strictSingleIndexNoExpandForbidClosed();

    /**
     * The concrete index name
     *
     * Whether index property is optional depends on the concrete implementation. If index property is required the
     * concrete implementation should use {@link #validateNonNullIndex()} to check if the index property has been set
     */
    @Nullable
    protected String index;
    ShardId internalShardId;

    public SingleShardRequest() {
    }

    public SingleShardRequest(StreamInput in) throws IOException {
        super(in);
        if (in.readBoolean()) {
            internalShardId = new ShardId(in);
        }
        index = in.readOptionalString();
        // no need to pass threading over the network, they are always false when coming throw a thread pool
    }

    protected SingleShardRequest(String index) {
        this.index = index;
    }

    protected void validateNonNullIndex() {<FILL_FUNCTION_BODY>}

    /**
     * @return The concrete index this request is targeted for or <code>null</code> if index is optional.
     *         Whether index property is optional depends on the concrete implementation. If index property
     *         is required the concrete implementation should use {@link #validateNonNullIndex()} to check
     *         if the index property has been set
     */
    @Nullable
    public String index() {
        return index;
    }

    /**
     * Sets the index.
     */
    @SuppressWarnings("unchecked")
    public final Request index(String index) {
        this.index = index;
        return (Request) this;
    }

    @Override
    public String[] indices() {
        return new String[]{index};
    }

    @Override
    public IndicesOptions indicesOptions() {
        return INDICES_OPTIONS;
    }

    @Override
    public void writeTo(StreamOutput out) throws IOException {
        super.writeTo(out);
        out.writeOptionalWriteable(internalShardId);
        out.writeOptionalString(index);
    }
}

        if (index == null) {
            throw new IllegalArgumentException("index is missing");
        }
    
<methods>public void <init>() ,public void <init>(org.elasticsearch.common.io.stream.StreamInput) throws java.io.IOException,public org.elasticsearch.tasks.TaskId getParentTask() ,public void setParentTask(org.elasticsearch.tasks.TaskId) ,public void writeTo(org.elasticsearch.common.io.stream.StreamOutput) throws java.io.IOException<variables>private org.elasticsearch.tasks.TaskId parentTaskId