- [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.

} else {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < arr.length; ++i) {
                if (i > 0) {
                    sb.append(delim);
                }
                sb.append(arr[i]);
            }
            return sb.toString();
        }
    }
    public static String deleteAny(String inString, String charsToDelete) {
        if (isNotEmpty(inString) && isNotEmpty(charsToDelete)) {
            StringBuilder sb = new StringBuilder(inString.length());
            for (int i = 0; i < inString.length(); ++i) {
                char c = inString.charAt(i);
                if (charsToDelete.indexOf(c) == -1) {
                    sb.append(c);
                }
            }
            return sb.toString();
        } else {
            return inString;
        }
    }
    public static String[] toStringArray(Collection<String> collection) {
        return (String[]) collection.toArray(new String[0]);
    }
    public static String nullSafeToString(Object obj) {
        if (obj == null) {