gulp-sass: IncludePaths not working

I can’t get includePaths working on version 2.3.2 of gulp-sass and 4.4.2 of node.

Here’s my gulpfile contents:

const SASS_FILES = ['./code/styles/main.scss'];
const SASS_INCLUDE_PATHS = [
  path.join(__dirname, '/node_modules/normalize-scss/sass/'),
  path.join(__dirname, '/node_modules/bourbon/app/assets/stylesheets/'),
  path.join(__dirname, '/node_modules/bourbon-neat/app/assets/stylesheets/'),
  path.join(__dirname, '/node_modules/susy/sass/')
];

gulp.task('styles', function() {
  return gulp.src(SASS_FILES)
    .pipe(sass({ includePaths: SASS_INCLUDE_PATHS }))
    .pipe(gulp.dest(BUILD_DEST));
});

The task runs without error, and scss files I have within ./code/styles/ are pulled in just fine, but it seems the includePaths imports are completely ignored. If I strip my main.scss back to the following, for example:

@import 'normalize';
// @import 'bourbon';
// @import 'neat';
// @import 'susy';

My output is a completely blank file.

Interestingly, if I import bourbon and neat I do get something in my output, just not what I’d expect:

html {
  box-sizing: border-box; }

*, *::after, *::before {
  box-sizing: inherit; }

Importing susy, again, yeilds no extra css added to the output.

Any advice anyone could offer would be much appreciated.