- [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.

sb.append(to.charAt(ix));
                }
            }
        }
        return sb == null ? src : sb.toString();
    }
    /**
     * split.
     *
     * @param ch char.
     * @return string array.
     */
    public static String[] split(String str, char ch) {
        List<String> list = null;
        char c;
        int ix = 0, len = str.length();
        for (int i = 0; i < len; i++) {
            c = str.charAt(i);
            if (c == ch) {
                if (list == null) {
                    list = new ArrayList<String>();
                }
                list.add(str.substring(ix, i));
                ix = i + 1;
            }
        }
        if (ix > 0) {
            list.add(str.substring(ix));
        }
        return list == null ? EMPTY_STRING_ARRAY : (String[]) list.toArray(EMPTY_STRING_ARRAY);