default StringBuilder appendQueryString(StringBuilder buf) {
        requireNonNull(buf, "buf");
        QueryStringEncoder.encodeParams(buf, this);
        return buf;
    }
Encodes all parameter entries into a query string, as defined in
<a href="https://www.w3.org/TR/2014/REC-html5-20141028/forms.html#url-encoded-form-data">4.10.22.6,
HTML5 W3C Recommendation</a>, and appends it into the specified {@link StringBuilder}.

@return the specified {@link StringBuilder} for method chaining.
core/src/main/java/com/linecorp/armeria/common/QueryParamGetters.java