Cannot resolve method 'add(TagKey <Block>)'

[jolly comet]

So I am watching this tutorial

https://www.youtube.com/watch?v=kbciFlIMhCs

and im at 8:51 and when he writes

getOrCreateTagBuilder(ModTags.Blocks.NEEDS_RUBY_TOOL)
                .add(BlockTags.NEEDS_IRON_TOOL);

which I do aswell. but for some reason I get an error. any reason why?

[jolly comet]

?