code: public Iterator<String> getPrefixes(final String namespaceURI) {
          if (namespaceURI == null) {
              // Be compliant with the JAXB contract for NamespaceResolver.
              throw new IllegalArgumentException("Cannot acquire prefixes for null namespaceURI.");
          }
  
          return Collections.singletonList(uri2Prefix.get(namespaceURI)).iterator();
      }
docs: {@inheritDoc}