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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" ... >`


boolean applyToRollback = child.getChildValue(null, "applyToRollback", false);
                Set<String> dbms = new HashSet<>();
                if (dbmsString != null) {
                    dbms.addAll(StringUtil.splitAndTrim(dbmsString, ","));
                }
                ContextExpression context = null;
                if (contextString != null) {
                    context = new ContextExpression(contextString);
                }
                Labels labels = null;
                if (labelsString != null) {
                    labels = new Labels(labelsString);
                }
                List<ParsedNode> potentialVisitors = child.getChildren();
                for (ParsedNode node : potentialVisitors) {
                    SqlVisitor sqlVisitor = SqlVisitorFactory.getInstance().create(node.getName());
                    if (sqlVisitor != null) {
                        sqlVisitor.setApplyToRollback(applyToRollback);
                        if (!dbms.isEmpty()) {
                            sqlVisitor.setApplicableDbms(dbms);
                        }
                        sqlVisitor.setContexts(context);
                        sqlVisitor.setLabels(labels);
                        sqlVisitor.load(node, resourceAccessor);
                        addSqlVisitor(sqlVisitor);
                    }
                }
                break;
            case "preConditions":
                this.preconditions = new PreconditionContainer();