title: proguard problem after updating to android gradle plugin 3.5
body: <p>I save the <code>json</code> presentation of some objects as cache in my app. I had no problem after updating each release of the app and <code>json</code> objects was correctly converted to java objects. After updating to android gradle plugin 3.5 (Adding this line):</p>
  
  <pre><code>classpath 'com.android.tools.build:gradle:3.5.0'
  </code></pre>
  
  <p>When I create the release apk, It seems that it can't convert the <code>json</code> string to java objects and it seems that the obfuscated names has changed. When I revert it to gradle plugin 3.4.2, everything is OK. So what is the problem and how can I fix that?</p>