@Override
            public Boolean apply(Long key, Integer value) {
                if (first) {
                    first = false;
                } else {
                    buf.append(", ");
                }
                buf.append(key);
                buf.append("=");
                buf.append(value);
                return true;
            }
Look until FREE slot or we start to loop
core/src/main/java/com/alibaba/fastjson2/internal/trove/map/hash/TLongIntHashMap.java