code: @Deprecated
      @NotNull
      public static <T> Collector<T, ?, Double> averaging(@NotNull final Function<? super T, Double> mapper) {
          return averagingDouble(new ToDoubleFunction<T>() {
  
              @Override
              public double applyAsDouble(T t) {
                  return mapper.apply(t);
              }
          });
      }
docs: Returns a {@code Collector} that calculates average of input elements.
  
  @param <T> the type of the input elements
  @param mapper  the mapping function which extracts value from element to calculate result
  @deprecated  As of release 1.1.3, replaced by
  {@link #averagingDouble(com.annimon.stream.function.ToDoubleFunction)}
  @return a {@code Collector}