addTags(span, key, value, prefix) {
		const name = prefix ? `${prefix}.${key}` : key;
		if (value != null && typeof value == "object") {
			Object.keys(value).forEach(k => this.addTags(span, k, value[k], name));
		} else if (value !== undefined) {
			span.setTag(name, value);
		}
	}
Add tags to span

@param {Object} span
@param {String} key
@param {any} value
@param {String?} prefix