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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" ... >`


}
        @Override
        public String toString() {
            return key;
        }
    }
    protected String key;
    private ChangeLogParameters changeLogParameters;
    /**
     * List of change objects defined in this changeset
     */
    private List<Change> changes;
    /**
     * "id" specified in changeLog file.  Combination of id+author+filePath must be unique
     */
    private String id;
    /**
     * "author" defined in changeLog file.  Having each developer use a unique author tag allows duplicates of "id" attributes between developers.
     */
    private String author;
    /**
     * File changeSet is defined in.  May be a logical/non-physical string.  It is included in the unique identifier to allow duplicate id+author combinations in different files
     */
    private String filePath = "UNKNOWN CHANGE LOG";
    /**
     * File path stored in the databasechangelog table. It should be the same as filePath, but not always.
     */
    private String storedFilePath;
    /**
     * If set to true, the changeSet will be executed on every update. Defaults to false