Some of the `case` statement expressions span multiple lines, but it's not necessary to wrap them in curly braces, since they're fairly clear to follow?
The Scala style guide does mention that curly braces should be used if there's any muti-lined expression, but it's a bit ambiguous for cases where there's a single expression that requires line wrapping...
Most of the Twitter code (e.g, algebird) omits curly braces for similar code structures like this.