title: Obfuscating the .aar files
body: <p>I have created the .aar file (containing the resources &amp; drawables) of an Android library project using </p>
  
  <pre><code>./gradlew assemble
  </code></pre>
  
  <p>I have enabled obfuscating by setting minify == true</p>
  
  <pre><code>buildTypes {
          release {
              minifyEnabled true
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
      }
  </code></pre>
  
  <p>However when I run the mentioned gradle command with minify enabled = true, I get <code>java.io.IOException: The output jar is empty. Did you specify the proper '-keep' options?</code></p>
  
  <p>What does this error pointing to and how can I obfuscate the library .aar file?</p>
  
  <p>Best Regards</p>