title: Why do I get white screen when building flutter web
body: <p>I want to build a flutter web app, so I enter 'webdev build' command and after the operation finishes, I open the 'index.html' file located in build directory and it's just a white screen.
  I tried it on a fresh project and the problem persists.
  There's no problem during developing.</p>
  
  <p><a href="https://i.stack.imgur.com/IpSNy.png" rel="noreferrer"><img src="https://i.stack.imgur.com/IpSNy.png" alt="enter image description here"></a></p>
  
  <p>Here's my flutter doctor output:</p>
  
  <pre><code>Doctor summary (to see all details, run flutter doctor -v):
  [√] Flutter (Channel stable, v1.5.4-hotfix.2, on Microsoft Windows [Version 10.0.17134.766], locale en-US)
  
  [√] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
  [√] Android Studio (version 3.3)
  [√] VS Code (version 1.35.1)
  [!] Connected device
      ! No devices available
  
  ! Doctor found issues in 1 category.
  </code></pre>