console.log(Object.keys(params).filter(key => params[key]).reduce((p, key) =>  p.append(key, params[key]),              new HttpParams())); //work
console.log(Object.keys(params).filter(key => params[key]).reduce((p, key) => {p.append(key, params[key]); return p; }, new HttpParams())); //not work

第一行返回值控制台输出正常。
第二行返回值控制台输出时没有写入参数。

HttpParams {updates: Array(2), cloneFrom: HttpParams, encoder: HttpUrlEncodingCodec, map: null}
HttpParams {updates: null, cloneFrom: null, encoder: HttpUrlEncodingCodec, map: null}