- [x] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.
- [x] I have checked the [FAQ](https://github.com/apache/dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.7.4
* Operating System version: Darwin Kernel Version 18.7.0
* Java version: 1.8.0_181-b13)

### Steps to reproduce this issue

1. invoke `StringUtils.split("d,1,2,4", 'a')`
2. invoke `"d,1,2,4".split("a")`

Pls. provide [GitHub address] to reproduce this issue.

### Expected Result

`StringUtils.split("d,1,2,4", 'a')` should return `["d,1,2,4"]` just like `"d,1,2,4".split("a")`.

### Actual Result

empty array.

return map;
    }
    public static String getQueryStringValue(String qs, String key) {
        Map<String, String> map = StringUtils.parseQueryString(qs);
        return map.get(key);
    }
    /**
     * parse query string to Parameters.
     *
     * @param qs query string.
     * @return Parameters instance.
     */
    public static Map<String, String> parseQueryString(String qs) {
        if (isEmpty(qs)) {
            return new HashMap<String, String>();
        }
        return parseKeyValuePair(qs, "\\&");
    }
    public static String getServiceKey(Map<String, String> ps) {
        StringBuilder buf = new StringBuilder();
        String group = ps.get(GROUP_KEY);
        if (isNotEmpty(group)) {
            buf.append(group).append("/");
        }
        buf.append(ps.get(INTERFACE_KEY));
        String version = ps.get(VERSION_KEY);
        if (isNotEmpty(group)) {
            buf.append(":").append(version);
        }
        return buf.toString();