As @sterretje and @van_der_decken mentioned, you should have set all warnings reported and try to eliminate each and everyone of them in your code.
In Core are also some warnings, but the code works there somehow anyway and it is too complicate to fix even for advanced programmers and may introduce other problems.
I also have always set all warnings to Always.
It proved to me, that fixing all warnings is way faster, then fixing problem introduced by hiding warnings.
And in this case it would helped too, as the compiler would complain about this typo (missing parentheses or round brackets) as about type warning.
(And as we discussed here, this wrong type is easy to do with millis or other simply functions, but way harder to do with Serial.println or other more complicated functions.)