title: compileDebugJava - is not incremental. Unable to infer the source directories
body: <p>Since Gradle 2.1, incremental compilation of Java source is now supported <a href="http://gradle.org/docs/current/userguide/java_plugin.html#sec:incremental_compile" rel="nofollow">check this</a></p>
  
  <p>I used below snip of code to enable it</p>
  
  <pre><code>afterEvaluate {
  
      android.applicationVariants.each { variant -&gt;
          variant.javaCompile.options.incremental = true
      }
  }
  </code></pre>
  
  <p>But I am getting below warning message,</p>
  
  <blockquote>
    <p>:App:compileDebugJava - is not incremental. Unable to infer the source
    directories.</p>
  </blockquote>
  
  <p>Please suggest me what should I do to get rid of it</p>