Injected css about angular2-seed-sass HOT 5 CLOSED

function processExternalScss() {
  return gulp.src([
      join(APP_SRC, 'assets', '**', '*.scss'),  // assets/main.scss etc.
      getExternalCss().map(r => r.src)          // node_modules/.../*.css etc.
    ])
    .pipe(plugins.sass(SASS_OPTIONS))
    .pipe(isProd ? plugins.cached('process-external-css') : plugins.util.noop())
    .pipe(plugins.postcss(processors))
    .pipe(isProd ? plugins.concat(CSS_PROD_BUNDLE) : plugins.util.noop())
    .pipe(gulp.dest(CSS_DEST));
}

function getExternalCss() {
  return DEPENDENCIES.filter(d => /\.css$/.test(d.src));
}

function processExternalScss() {
  return merge(processAssetsCss(), processInjectedCss())
    .pipe(plugins.sass(SASS_OPTIONS))
    .pipe(isProd ? plugins.cached('process-external-css') : plugins.util.noop())
    .pipe(plugins.postcss(processors))
    .pipe(isProd ? plugins.concat(CSS_PROD_BUNDLE) : plugins.util.noop())
    .pipe(gulp.dest(CSS_DEST));
}

function processAssetsCss() {
  return gulp.src(join(APP_SRC, 'assets', '**', '*.scss'))
    .pipe(isProd ? plugins.cached('process-assets-css') : plugins.util.noop());
}

function processInjectedCss() {
  return gulp.src(getExternalCss().map(r => r.src))
    .pipe(isProd ? plugins.cached('process-injected-css') : plugins.util.noop());
}

function getExternalCss() {
  return DEPENDENCIES.filter(d => /\.css$/.test(d.src));
}

TSError: ⨯ Unable to compile TypeScript
tools/tasks/seed/build.scss.ts (51,19): Argument of type '(string | string[])[]' is not assignable to parameter of type 'string | string[]'.