What 'subtle' bug ?

It returns 'email' instead of 'emails' which I assume was a typo, which of course the compiler would complain about, are you claiming that a variable name typo is somehow a 'subtle bug' ?

Only other thing I see directly is that 'users' is undefined, but this is a code snippet after all, not a working program.

I think kaoD's point is that more code will always produce more errors, and more code (in the name of "readability") can give more surface area for bugs.

But that would be caught by the compiler. The error would be variable not defined.