code: @Override
  	public <T> AppEngineUpdate<E> set(Property<?, T> property, T value) {
  		if (property == null) {
  			throw new IllegalArgumentException("'property' must not be [" + property + "]");
  		}
  		
  		properties.put(property, value); 
  		return this;
  	}
docs: Qualifies property and the value to be updated.
  
  @param property The property to be updated by this
  {@code Update}.
  @param value The property value to be updated to.
  @return The {@code Update} to update the specified entity
  properties.