These hypotheses are different: that you will have zero effect, and that you will have some effect of unknown sign and magnitude, with expected value of zero. I object to the former, not necessarily to the latter (note that the expected absolute value of the effect is bound to be non-zero in the latter case). To give an estimate of the nature of the effect, we need to consider specific reasons that moved your decision.
These hypotheses are different: that you will have zero effect, and that you will have some effect of unknown sign and magnitude, with expected value of zero. I object to the former, not necessarily to the latter (note that the expected absolute value of the effect is bound to be non-zero in the latter case). To give an estimate of the nature of the effect, we need to consider specific reasons that moved your decision.