resetItem(item, timestamp) {
		item.timestamp = timestamp == null ? Date.now() : timestamp;
		item.sum = 0;
		item.count = 0;
		item.lastValue = null;

		if (this.buckets) {
			item.bucketValues = this.createBucketValues();
		}

		if (this.quantiles) {
			item.quantileValues = new TimeWindowQuantiles(
				this,
				this.quantiles,
				this.maxAgeSeconds,
				this.ageBuckets
			);
		}

		return item;
	}
Reset value of item.

@param {Object} item
@param {Number?} timestamp