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## Environment
**Liquibase Version**:  4.1

**Liquibase Integration & Version**: gradle

**Liquibase Extension(s) & Version**: 

**Database Vendor & Version**: any 

**Operating System Type & Version**: Win10, Java8

## Description
If you add two dbms to a changeset, it seperates them with ',xxx' instead of ','. Therefore the second dbms will not be correctly recognized.

 `<changeSet  dbms="oracle,xxxmssql" ... >`

## Steps To Reproduce
JUnit-Test to reproduce: 

```
  @Test
  void testLiquibaseXmlBug() throws IOException {
    ByteArrayOutputStream stream = new ByteArrayOutputStream();
    DatabaseChangeLog log = new DatabaseChangeLog();
    ChangeLogSerializer serializer = new XMLChangeLogSerializer();
    ChangeSet set = new ChangeSet("Test", "test", Boolean.FALSE, Boolean.FALSE, null, "context", "oracle, mssql",log);
    List<ChangeLogChild> changes = new ArrayList<>();
    changes.add(set);
    serializer.write(changes, stream);
    assertEquals("<?xml version=\"1.1\" encoding=\"UTF-8\" standalone=\"no\"?>"
                 + "<databaseChangeLog xmlns=\"http://www.liquibase.org/xml/ns/dbchangelog\" xmlns:ext=\"http://www.liquibase.org/xml/ns/dbchangelog-ext\" xmlns:pro=\"http://www.liquibase.org/xml/ns/pro\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xsi:schemaLocation=\"http://www.liquibase.org/xml/ns/dbchangelog-ext http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-ext.xsd http://www.liquibase.org/xml/ns/pro http://www.liquibase.org/xml/ns/pro/liquibase-pro-4.1.xsd http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-4.1.xsd\">"
                 + "    <changeSet author=\"test\" context=\"context\" dbms=\"oracle,mssql\" id=\"Test\" objectQuotingStrategy=\"LEGACY\"/>"
                 + "</databaseChangeLog>", new String(stream.toByteArray()));
  }
```

## Expected/Desired Behavior
Changelog should look like: 
 `<changeSet  dbms="oracle,mssql" ... >`


}
    public String getComments() {
        return comments;
    }
    public void setComments(String comments) {
        this.comments = comments;
    }
    public boolean isAlwaysRun() {
        return alwaysRun;
    }
    public boolean isRunOnChange() {
        return runOnChange;
    }
    public boolean isRunInTransaction() {
        return runInTransaction;
    }
    public RollbackContainer getRollback() {
        return rollback;
    }
    public void addRollBackSQL(String sql) {
        if (StringUtil.trimToNull(sql) == null) {
            if (rollback.getChanges().isEmpty()) {
                rollback.getChanges().add(new EmptyChange());
            }
            return;
        }
        for (String statment : StringUtil.splitSQL(sql, null)) {
            rollback.getChanges().add(new RawSQLChange(statment.trim()));
        }
    }