Map<String,MyModel> result = new HashMap<>();

public static void main(String[] argu[]) {
	new TestGenerics().createValue("1").setValue("1VAL").build().createValue("2").setValue("2VAL").build().extendValue("1").setValue("1WAL-Override").build();
}

public MyModelBuilder<TestGenerics> createValue(String key) {
	return new MyModelBuilder<>(this, new MyModel(), (p,v) -> p.result.put(v.key, v)).setKey(key);
}

public MyModelBuilder<TestGenerics> extendValue(String key) {
	return new MyModelBuilder<>(this, result.get(key), (p,v) -> {});
}

public class MyModel {
	String key;
	String value;
}

public interface Builder<T> {
	T build();
}

/**
 * Abstract object builder with parent builder.
 *
 * @param <P> The parent builder.
 * @param <T> The object to build.
 * @param <B> The current builder.
 */
abstract public class AbstractBuilder<P, T, B> implements Builder<P> {
	private final P parent;
	private final T value;
	private final BiConsumer<P, T> parentBuilder;
	
	public AbstractBuilder(P parent, T value, BiConsumer<P, T> parentBuilder) {
		this.parent = parent;
		this.value = value;
		this.parentBuilder = parentBuilder;
	}
	
	@Override
	public final P build() {
		parentBuilder.accept(parent, value);
		return parent;
	}
	
	protected final B make(Consumer<T> mixer) {
		mixer.accept(value);
		return (B) this;
	}
}

public class MyModelBuilder<P> extends AbstractBuilder<P,MyModel,MyModelBuilder<P>> {
	public MyModelBuilder(P parent, MyModel value, BiConsumer<P, MyModel> parentBuilder) {
		super(parent, value, parentBuilder);
	}
	
	protected MyModelBuilder<P> setKey(String key) {
		return make(v -> v.key=key);
	}
	
	public MyModelBuilder<P> setValue(String value) {
		return make(v -> v.value=value);
	}
}

javadoc: error - In doclet class info.leadinglight.umljavadoclet.UmlJavaDoclet,  method start has thrown an exception java.lang.reflect.InvocationTargetException
java.lang.StringIndexOutOfBoundsException: String index out of range: -1
	at java.lang.String.substring(String.java:1967)
	at info.leadinglight.umljavadoclet.model.ModelPackage.parentPackageFullName(ModelPackage.java:62)
	at info.leadinglight.umljavadoclet.model.Model.isRootPackage(Model.java:87)
	at info.leadinglight.umljavadoclet.model.Model.rootPackages(Model.java:75)
	at info.leadinglight.umljavadoclet.printer.OverviewDiagramPrinter.generate(OverviewDiagramPrinter.java:20)
	at info.leadinglight.umljavadoclet.UmlJavaDoclet.generateOverviewDiagram(UmlJavaDoclet.java:173)
	at info.leadinglight.umljavadoclet.UmlJavaDoclet.start(UmlJavaDoclet.java:75)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.sun.tools.javadoc.DocletInvoker.invoke(DocletInvoker.java:310)
	at com.sun.tools.javadoc.DocletInvoker.start(DocletInvoker.java:189)
	at com.sun.tools.javadoc.Start.parseAndExecute(Start.java:366)
	at com.sun.tools.javadoc.Start.begin(Start.java:219)
	at com.sun.tools.javadoc.Start.begin(Start.java:205)
	at com.sun.tools.javadoc.Main.execute(Main.java:64)
	at com.sun.tools.javadoc.Main.main(Main.java:54)