hashingLabels(labels) {
		if (this.labelNames.length == 0 || labels == null || typeof labels !== "object") return "";

		const parts = [];
		for (let i = 0; i < this.labelNames.length; i++) {
			const v = labels[this.labelNames[i]];
			if (typeof v == "number") parts.push(v);
			else if (typeof v === "string") parts.push('"' + v + '"');
			else if (typeof v === "boolean") parts.push("" + v);
			else parts.push("");
		}
		return parts.join("|");
	}
Create a hash from label values. It will
be used as a key in Map.

@param {Object} labels
@returns {String}
@memberof BaseMetric