liquibase-core/src/main/java/liquibase/database/DatabaseFactory.java
public List<Database> getInternalDatabases() {
        List<Database> returnList = new ArrayList<>();
        for (SortedSet<Database> set : internalDatabases.values()) {
            returnList.add(set.iterator().next());
        }
        return returnList;
    }
public List<Database> getInternalDatabases() {
        List<Database> returnList = new ArrayList<>();
        for (SortedSet<Database> set : internalDatabases.values()) {
            returnList.add(set.iterator().next());
        }
        return returnList;
    }
Returns instances of all "internal" database types.