Inner dsl block example is not working or something missing

[vinz486]

This is all what I need to create a inner data extension block?

import java.io.File;
import org.gradle.api.Action;

public class SiteExtension {
    private File outputDir;
    private final CustomData customData = new CustomData();

    public void setOutputDir(File outputDir) {
        this.outputDir = outputDir;
    }

    public File getOutputDir() {
        return outputDir;
    }

    public CustomData getCustomData() {
        return customData;
    }

    public void customData(Action<? super CustomData> action) {
        action.execute(customData);
    }
}

(and a pojo CustomData class)

Who, when and how method "customData" is called?

Simply creating extension:
project.getExtensions().create("name", SiteExtension.class);

Does not work.

What should be done? In the whole Gradle guide is absolutely not clear.

[vinz486]

For reference: https://guides.gradle.org/implementing-gradle-plugins/#modeling_dsl_like_apis