Cyclic what ?

[Rémi Forax]

Maurizio,
This snippet emit a warning.
I don't understand why it doesn't just compile and why it emit a warning
and not an error.

  public interface Mapper<T, U> {
       public U map(T t);
  }

   public static <T,U,V> Mapper<T,V> compose(Mapper<? super T, ? extends 
U> mapper1,
      Mapper<? super U, ? extends V> mapper2) {
         return #{ t -> mapper2.map(mapper1.map(t)) };
   }

warning: thrown types cannot be inferred from lambda body because of 
cyclic inference
           return #{ t -> mapper2.map(mapper1.map(t)) };
                  ^
   explicit type required for the following parameter: t

Rémi