code: public void setValue(ELContext context, Object base, Object property,
              Object value) {
          if (context == null) {
              throw new NullPointerException();
          }
  
          if (base instanceof ResourceBundle) {
              context.setPropertyResolved(true);
              throw new PropertyNotWritableException(
                      "ResourceBundles are immutable");
          }
      }
docs: If the base object is a ResourceBundle, throw a
  {@link PropertyNotWritableException}.
  
  @param context
  The context of this evaluation.
  @param base
  The ResourceBundle to be modified. Only bases that are of type
  ResourceBundle are handled.
  @param property
  The String property to use.
  @param value
  The value to be set.
  @throws NullPointerException
  if context is <code>null</code>.
  @throws PropertyNotWritableException
  Always thrown if base is an instance of ReasourceBundle.