code: public static <T1, T2, R> BiFunction<T1, T2, R> spy2nd(BiFunction<T1, T2, R> function, Box<T2> param2) {
          return spy(function, Box.<R>empty(), Box.<T1>empty(), param2);
      }
docs: Proxies a binary function spying for second parameter.
  
  @param <T1> the function first parameter type
  @param <T2> the function second parameter type
  @param <R> the function result type
  @param function the function that will be spied
  @param param2 a box that will be containing the second spied parameter
  @return the proxied function