title: How to use gulp-if to conditionally compile less files?
body: <p>I can't get <a href="https://www.npmjs.org/package/gulp-if" rel="noreferrer">gulp-if</a> to work correctly.</p>
  
  <p>Without gulp-if it works fine:</p>
  
  <pre><code>gulp.task('css', function() {
      return gulp.src([
      //  'bower_components/bootstrap/dist/css/bootstrap.css',
          'app/stylesheets/main.less',
      ])
      .pipe(less({
          strictMath: true,
           strictUnits: true,
      }))
      .pipe(concat('all.css', {newLine: '\n'}))
      .pipe(prefixer('&gt; 1%'))
      .pipe(minifyCss())
      .pipe(gulp.dest('public/css'));
  });
  </code></pre>
  
  <p>But as soon as I add <code>gulp-if</code> into the mix, the <code>gulpif</code> pipe returns nothing when it returns to the main stream:</p>
  
  <pre><code>gulp.task('css', function() {
      return gulp.src([
          'bower_components/bootstrap/dist/css/bootstrap.css',
          'app/stylesheets/main.less',
      ])
  
          .pipe(gulpif(/\.less$/,less({
              strictMath: true,
              strictUnits: true,
          })))
          .pipe(concat('all.css', {newLine: '\n'}))
          .pipe(prefixer('&gt; 1%'))
          .pipe(minifyCss())
          .pipe(gulp.dest('public/css'));
  });
  </code></pre>
  
  <p>Why is that? What am I doing wrong? If I add some logs into the <code>gulp-if</code> source code I can see that the condition <em>is</em> passing.</p>