code: @Override
  	public Element setDefaults(Context context, Element self)
  			throws EvaluationException {
  
  		assert (context != null);
  		assert (self != null);
  
  		return baseType.setDefaults(context, self);
  	}
docs: This will call the setDefaults method of the base type with the given
  argument. NOTE: this method cannot be called with self equal to null. If
  the element doesn't exist, then the caller must extract the default value
  from this type as set the value. Afterwards, this method can be called.
  This is necessary because we cannot lookup the path on a null value.