async getMaintenanceJSONList(userID) {
        let result = {};
        for (let maintenanceID in this.maintenanceList) {
            result[maintenanceID] = await this.maintenanceList[maintenanceID].toJSON();
        }
        return result;
    }
Get a list of maintenances for the given user.
@param {string} userID - The ID of the user to get maintenances for.
@returns {Promise<object>} A promise that resolves to an object with maintenance IDs as keys and maintenances objects as values.