In production mode, that would not have the desired effect; cf. [Chap 2 of Up and Running](https://www.dartlang.org/docs/dart-up-and-running/contents/ch02.html#ch02-function-equality)
> When Dart expects a boolean value, only the value true is treated as true. All other values are treated as false.

Hence, for example, if `isFirstPass` were 1, then `!= false` would be true.