- [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.

assertEquals("dubbo.tag1.tag11", StringUtils.toURLKey("dubbo-tag1_tag11"));
    }
    @Test
    public void testToOSStyleKey() {
        assertEquals("DUBBO_TAG1", StringUtils.toOSStyleKey("dubbo_tag1"));
        assertEquals("DUBBO_TAG1", StringUtils.toOSStyleKey("dubbo.tag1"));
        assertEquals("DUBBO_TAG1_TAG11", StringUtils.toOSStyleKey("dubbo.tag1.tag11"));
        assertEquals("DUBBO_TAG1", StringUtils.toOSStyleKey("tag1"));
    }
    @Test
    public void testParseParameters() {
        String legalStr = "[{key1:value1},{key2:value2}]";
        Map<String, String> legalMap = StringUtils.parseParameters(legalStr);
        assertEquals(2, legalMap.size());
        assertEquals("value2", legalMap.get("key2"));
        String legalSpaceStr = "[{key1: value1}, {key2 :value2}]";
        Map<String, String> legalSpaceMap = StringUtils.parseParameters(legalSpaceStr);
        assertEquals(2, legalSpaceMap.size());
        assertEquals("value2", legalSpaceMap.get("key2"));
        String legalSpecialStr = "[{key-1: value*.1}, {key.2 :value*.-_2}]";
        Map<String, String> legalSpecialMap = StringUtils.parseParameters(legalSpecialStr);
        assertEquals(2, legalSpecialMap.size());
        assertEquals("value*.1", legalSpecialMap.get("key-1"));
        assertEquals("value*.-_2", legalSpecialMap.get("key.2"));
        String illegalStr = "[{key=value},{aa:bb}]";
        Map<String, String> illegalMap = StringUtils.parseParameters(illegalStr);
        assertEquals(0, illegalMap.size());
    }
}