code: @SafeVarargs
      public static JsonDocument toJsonDocument(final Object... a) {
          return a.length == 1 ? toJsonDocument(a[0], toJsonObject(a[0])) : toJsonDocument(a, toJsonObject(a));
      }
docs: The id for the target document is got from the "id" property in the specified <code>a</code>.
  
  @param a pairs of property name and value.
  @return
  @throws IllegalArgumentException if the specified <code>a</code> doesn't have any "id" property.