ImmutableDelight.java

@Value.Immutable 
@Value.Style(allParameters = true)
public abstract class Foo implements FooModel{
    public static final FooModel.Mapper<Foo> MAPPER = new FooModel.Mapper<>((Mapper.Creator<Foo>) ImmutableFoo::of);
    public static final class Marshal extends FooModel.FooMarshal {}
}

Strangely, it works for me without the cast. Both Javac and ECJ

@Value.Immutable 
@Value.Style(allParameters = true)
public abstract class Foo implements FooModel{
    public static final FooModel.Mapper<Foo> MAPPER = new FooModel.Mapper<>(ImmutableFoo::of);
    public static final class Marshal extends FooModel.FooMarshal {}
}