title: Error when compiling Less in Gulp: `File not found with singular glob`
body: <p>I'm working on a legacy site that has some pre-set-up Gulp commands.</p>
  <p>I want to compile some .less files into .css. The existing script is as such:</p>
  <pre><code>gulp.task('less', function(){
    return gulp.src('./src/css/less/app.less')
    .pipe(less({
      paths: [ path.join(__dirname, 'less', 'includes') ]
    }))
    .pipe(gulp.dest('./src/css/'))
  });
  </code></pre>
  <p>However, when I run this I get an error:</p>
  <pre><code>Error: File not found with singular glob: /src/css/less/app.less (if this was purposeful, use `allowEmpty` option)
  </code></pre>
  <p>I've checked all paths, all <code>@import</code> and directories and they're all ok.</p>
  <p>I am using Gulp Local: 4.0.0, CLI: 2.3.0.</p>
  <p>Would anyone know could be causing this?</p>