The easiest data to fake is null results because anything else is replicable, hence the importance of replication.
(The whole binary hypothesis system and culture is a mess though, but that's besides the point.)
However, I think that no one will do the scut work necessary to find that a null result was faked, and even if they do since you the researcher got very little status out of it then it’s believable that you made a mistake, and didn’t falsify data.