Personally I have a very strong prior that nudging must have an effect > 0 - it would just be extremely surprising to me if the effect of an intervention that clearly points in one direction would be exactly 0. This may however still be compatible with the effects in many cases being too small to be worth to put the spotlight on, and I suspect it just strongly depends on the individual case and intervention.
Just to note I wrote a separate post focusing on pretty much that last point: