Boilerplate code for GstAggregator

I want to create a custom plugin of type GstAggregator but I cannot generate the boilerplate code with gst-element-maker tool. I use aggregator as the base class name but the generation fails with the message: Template file for aggregator not found. Am I using a wrong base class name in the tool or there is another way to generate the boilerplate code? Thanks in advance!