Bitbucket server plugin code never reached

I am writing a plugin for Bitbucket which looks as follows:

package plantuml;

import com.atlassian.markup.renderer.MarkupRendererComponent;
import com.atlassian.markup.renderer.RenderContext;
import com.atlassian.markup.renderer.RenderTransform;
import javax.annotation.Nonnull;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class PlantUmlRendererComponentImpl implements MarkupRendererComponent {

    private static Logger logger = LoggerFactory.getLogger(PlantUmlRendererComponentImpl.class);


    public PlantUmlRendererComponentImpl() {

    }

    @Nonnull
    @Override
    public RenderTransform process(CharSequence charSequence, @Nonnull RenderContext renderContext) {
        RenderTransform.TransformBuilder builder = RenderTransform.builder();
        logger.info("in here");

        return builder.build();

    }
}

If I install this plugin and then load files which contain markup like README.md I would expect to see the log message ‘in here’, but I never see anything called…