How to use the node-opcua-data-value.TimestampsToReturn.Invalid function in node-opcua-data-value

* If maxAge is set to the max Int32 value or greater, the Server shall attempt to get a cached value.
 * Negative values are invalid for maxAge.
 * @class ReadRequest
 */

const Obsolete_ReadRequest_schema = {
    name: "ReadRequest",
    fields: [
        {   name: "requestHeader" ,               fieldType: "RequestHeader"},

        {   name: "maxAge",                       fieldType: "Duration",
            documentation: "Maximum age of the value to be read in milliseconds"
        },
        {   name: "timestampsToReturn" ,          fieldType: "TimestampsToReturn",
            documentation:"An enumeration that specifies the Timestamps to be returned for each requested Variable Value Attribute.",
            defaultValue: TimestampsToReturn.Invalid
        },
        { name: "nodesToRead", isArray:true,    fieldType: "ReadValueId",
            documentation: "List of Nodes and their Attributes to read. For each entry in this list, a StatusCode is " +
            "returned, and if it indicates success, the Attribute Value is also returned."
        }
    ]
};
exports.ReadRequest_Schema = Obsolete_ReadRequest_schema;