- [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.

}
    public static String toQueryString(Map<String, String> ps) {
        StringBuilder buf = new StringBuilder();
        if (ps != null && ps.size() > 0) {
            for (Map.Entry<String, String> entry : new TreeMap<String, String>(ps).entrySet()) {
                String key = entry.getKey();
                String value = entry.getValue();
                if (isNoneEmpty(key, value)) {
                    if (buf.length() > 0) {
                        buf.append("&");
                    }
                    buf.append(key);
                    buf.append("=");
                    buf.append(value);
                }
            }
        }
        return buf.toString();
    }
    public static String camelToSplitName(String camelName, String split) {
        if (isEmpty(camelName)) {
            return camelName;
        }
        StringBuilder buf = null;
        for (int i = 0; i < camelName.length(); i++) {
            char ch = camelName.charAt(i);
            if (ch >= 'A' && ch <= 'Z') {
                if (buf == null) {
                    buf = new StringBuilder();
                    if (i > 0) {