title: How do you create an empty stream in Gulp?
body: <p>SSCCE:</p>
  
  <pre><code>gulp.task('foo', [], function() {
      var barFiles = getBarFiles();
      var bazFiles = getBazFiles();
  
      var barStream, bazStream;
      if (barFiles &amp;&amp; barFiles.length &gt; 0) {
          barStream = gulp.src(barFiles);
      }
      if (bazStream &amp;&amp; bazStream.length &gt; 0) {
          bazStream = gulp.src(bazStream);
      }
      return eventStream
          .merge(barStream, bazStream)
          .pipe(g.concat('bar-and-baz'))
          .pipe(gulp.dest('./foo-output/'));
  });
  </code></pre>
  
  <p><code>getBarFiles()</code> or <code>getBazFiles()</code> may return an empty array,
  which is <em>not</em> allowed by <code>gulp.src()</code>: <code>Error: Invalid glob argument</code>,
  hence the need to wrap the creation of the stream with an <code>if</code> condition.</p>
  
  <p>So the question is, how do I create an empty stream,
  so that it can be merged with the other empty on non-empty stream?</p>