How to use the coap/common.ContentFormat.PlainText function in coap

send(response, session) {
		let contentFormat = ContentFormat.OctetStream;
		switch (typeof response) {
			case 'string':
				response = ArrayBuffer.fromString(response);
				contentFormat = ContentFormat.PlainText;
				// fallthrough
			case 'object':
				if (response instanceof ArrayBuffer) {
					response = session.createResponse(response, contentFormat);
				}
				break;
		}

		response.token = session.token;
		if (!response.code) response.code = [2, 5];

		if (!response.options) response.options = [];

		if (session.confirmable && !session.response && !session.ackSent) {
			response.type = Type.Ack;
			response.messageId = session.messageId;