- [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.

assertThat(StringUtils.stripEnd("abc", null), equalTo("abc"));
        assertThat(StringUtils.stripEnd("  abc", null), equalTo("  abc"));
        assertThat(StringUtils.stripEnd("abc  ", null), equalTo("abc"));
        assertThat(StringUtils.stripEnd(" abc ", null), equalTo(" abc"));
        assertThat(StringUtils.stripEnd("  abcyx", "xyz"), equalTo("  abc"));
        assertThat(StringUtils.stripEnd("120.00", ".0"), equalTo("12"));
    }
    @Test
    public void testReplace() throws Exception {
        assertThat(StringUtils.replace(null, "*", "*"), nullValue());
        assertThat(StringUtils.replace("", "*", "*"), equalTo(""));
        assertThat(StringUtils.replace("any", null, "*"), equalTo("any"));
        assertThat(StringUtils.replace("any", "*", null), equalTo("any"));
        assertThat(StringUtils.replace("any", "", "*"), equalTo("any"));
        assertThat(StringUtils.replace("aba", "a", null), equalTo("aba"));
        assertThat(StringUtils.replace("aba", "a", ""), equalTo("b"));
        assertThat(StringUtils.replace("aba", "a", "z"), equalTo("zbz"));
        assertThat(StringUtils.replace(null, "*", "*", 64), nullValue());
        assertThat(StringUtils.replace("", "*", "*", 64), equalTo(""));
        assertThat(StringUtils.replace("any", null, "*", 64), equalTo("any"));
        assertThat(StringUtils.replace("any", "*", null, 64), equalTo("any"));
        assertThat(StringUtils.replace("any", "", "*", 64), equalTo("any"));
        assertThat(StringUtils.replace("any", "*", "*", 0), equalTo("any"));
        assertThat(StringUtils.replace("abaa", "a", null, -1), equalTo("abaa"));
        assertThat(StringUtils.replace("abaa", "a", "", -1), equalTo("b"));
        assertThat(StringUtils.replace("abaa", "a", "z", 0), equalTo("abaa"));
        assertThat(StringUtils.replace("abaa", "a", "z", 1), equalTo("zbaa"));
        assertThat(StringUtils.replace("abaa", "a", "z", 2), equalTo("zbza"));
    }
    @Test