private Set<QName> filterDefaultNamespace(Set<QName> _set) {
            final Set<QName> set = new HashSet<>(_set);
            for (Iterator<QName> it = set.iterator(); it.hasNext();) {
                final QName name = it.next();
                final String prefix = name.getPrefix();
                if (prefix == null || prefix.length() == 0) {
                    final String uri = name.getNamespaceURI();
                    if (uri != null && uri.length() > 0) {
                        final String assignedPrefix = myNamespaceContext.getPrefixForURI(uri, null);
                        if (assignedPrefix == null) {
                            it.remove();
                        }
                    }
                }
            }
            return set;
        }
private Set<QName> filterDefaultNamespace(Set<QName> _set)