Gulp выдаёт The following tasks did not complete: sass. Did you forget to signal async completion?

Question

[Denis1111]

(function(r){
	let gulp = r('gulp'),
		sass = r('gulp-sass');

	gulp.task('sass', function() {
		return gulp.src('./css/**/*.scss')
			.pipe(sass())
			.pipe(gulp.dest('dist/'));
	});
}(require));

Gulp выдаёт The following tasks did not complete: sass. Did you forget to signal async completion?
Почему?