code: public SmartHandle returnValue(Class<?> type, Object value) {
          return new SmartHandle(signature.changeReturn(type), MethodHandles.filterReturnValue(handle, MethodHandles.constant(type, value)));
      }
docs: Replace the return value with the given value, performing no other
  processing of the original value.
  
  @param type the type for the new return value
  @param value the new value to return
  @return a new SmartHandle that returns the given value