exports.UserError = class extends Error {
    constructor(message) {
        super(message);
        this.name = 'UserError';
        this.statusCode = 400;
    }
};

exports.getFinalState = function(ctx) {
    if (ctx.isNewInstance)
        return ctx.instance;
    if (ctx.currentInstance)
        return Object.assign({},
            ctx.currentInstance.__data,
            ctx.data || ctx.instance
        );

    return null;
};

exports.isMultiple = function(ctx) {
    return !ctx.isNewInstance && !ctx.currentInstance;
};