code: public static <KeyIn, ValueIn, ValueOut> Supplier<KeyIn, ValueIn, ValueOut> all() {
          return new AcceptAllSupplier(null);
      }
docs: The predefined Supplier selects all values and does not perform any kind of data
  transformation. Input value types need to match the aggregations expected value
  type to make this Supplier work.
  
  @param <KeyIn>    the input key type
  @param <ValueIn>  the input value type
  @param <ValueOut> the supplied value type
  @return all values from the underlying data structure as stored