As listed on this page: https://gohugo.io/overview/configuration/
Version: 0.25.1 and also 0.22-DEV, same issue in both
Which must mean you have something other stuff going on, hard to say with so little info, but I will guess that you have put your disableHugoGeneratorInject after a TOML map and by that made it non-existant.
On an added note:
Why would you want to disable this? It is only injected on the home page if no generator is present, and should be very little to ask in return for this free piece of software.