- [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 void testIsBlank() throws Exception {
        assertTrue(StringUtils.isBlank(null));
        assertTrue(StringUtils.isBlank(""));
        assertFalse(StringUtils.isBlank("abc"));
    }
    @Test
    public void testIsEmpty() throws Exception {
        assertTrue(StringUtils.isEmpty(null));
        assertTrue(StringUtils.isEmpty(""));
        assertFalse(StringUtils.isEmpty("abc"));
    }
    @Test
    public void testIsNoneEmpty() throws Exception {
        assertFalse(StringUtils.isNoneEmpty(null));
        assertFalse(StringUtils.isNoneEmpty(""));
        assertTrue(StringUtils.isNoneEmpty(" "));
        assertTrue(StringUtils.isNoneEmpty("abc"));
        assertTrue(StringUtils.isNoneEmpty("abc", "def"));
        assertFalse(StringUtils.isNoneEmpty("abc", null));
        assertFalse(StringUtils.isNoneEmpty("abc", ""));
        assertTrue(StringUtils.isNoneEmpty("abc", " "));
    }
    @Test
    public void testIsAnyEmpty() throws Exception {
        assertTrue(StringUtils.isAnyEmpty(null));
        assertTrue(StringUtils.isAnyEmpty(""));
        assertFalse(StringUtils.isAnyEmpty(" "));
        assertFalse(StringUtils.isAnyEmpty("abc"));
        assertFalse(StringUtils.isAnyEmpty("abc", "def"));
        assertTrue(StringUtils.isAnyEmpty("abc", null));