/**
  * Set or remove the type URI for a given custom primitive.
  *
  * @param custom Custom primitive.
  * @param The type URI.
  */
 public static void setTypeURI(CustomPrimitive custom, URI uri) {
   String value = (uri == null) ? null : uri.toString();
   PropertyHelper.setOrRemove(custom, TYPE_URI_KEY, value);
 }
 /**
  * Get the type URI for a given custom primitive or <code>null</code> if the type property is not
  * set.
  *
  * @param custom Custom primitive.
  * @return The type URI.
  */
 public static URI getTypeURI(CustomPrimitive custom) {
   String value = PropertyHelper.getFirstValue(custom, TYPE_URI_KEY);
   return (value != null) ? URI.createURI(value) : null;
 }