function parsePayload(error, rulePayload)
        {
            if (error || !rulePayload)
                return null;
            this._domModel.markUndoableState();
            this._fireStyleSheetChanged(styleSheetId);
            return new WebInspector.CSSRule(this, rulePayload);
        }
@param {?Protocol.Error} error
@param {?CSSAgent.CSSRule} rulePayload
@return {?WebInspector.CSSRule}
@this {WebInspector.CSSStyleModel}