- [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.

if (value.equals(v)) {
                    return true;
                }
            }
        }
        return false;
    }
    public static boolean isNumeric(String str, boolean allowDot) {
        if (str == null || str.isEmpty()) {
            return false;
        }
        boolean hasDot = false;
        int sz = str.length();
        for (int i = 0; i < sz; i++) {
            if (str.charAt(i) == '.') {
                if (hasDot || !allowDot) {
                    return false;
                }
                hasDot = true;
                continue;
            }
            if (!Character.isDigit(str.charAt(i))) {
                return false;
            }
        }
        return true;
    }
    /**
     * @param e
     * @return string