public LinkedHashSet<String> getSectionKeys() {
    return sectionKeys;
  }
Gets the collection of section names that was used to initialize this
{@link RoleCommandOrder} instance. If this instance has not been
initialized, this will be {@code null}.
<p/>
The ordering of this collection is maintained.

@return the section keys used to initialize this instance or {@code null}
        if it has not been initialized.
ambari-server/src/main/java/org/apache/ambari/server/metadata/RoleCommandOrder.java