"Error on drop of custom operator"
I'm learning to write custom operators. I followed the steps in the manual and customized some code from reading the source of existing operators. I wrote an ExampleSetWriter following the manual, called it ExSetWriter. Here's the screenshot of the error I get when I drag and drop my custom operator onto the canvas. What does this mean? What is null? Does it have anything to do with specifying a factory in the xml file?