title: Data binding expression not compiling
body: <p>I'm trying out the new data binding library. I have a weird issue where binding the <code>visibility</code> property is not compiling.</p>
  
  <p>This is a simplified version of the xml file:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;layout xmlns:android="http://schemas.android.com/apk/res/android"&gt;
  
      &lt;data&gt;
  
      &lt;variable
          name="header"
          type="com.example.EmailHeader" /&gt;
      &lt;/data&gt;
  
      &lt;RelativeLayout ... &gt;
  
          &lt;TextView
              ...
              android:text="@{header.senderName ?? header.senderAddress}"
              android:visibility="@{header.hasAttachment ? View.VISIBLE : View.INVISIBLE}" /&gt;
  
      &lt;/RelativeLayout&gt;
  &lt;/layout&gt;
  </code></pre>
  
  <p>I get the follow message when compiling:</p>
  
  <pre><code>Error:Execution failed for task ':app:compileDebugJavaWithJavac'.
  </code></pre>
  
  <blockquote>
    <p>java.lang.RuntimeException: Found data binding errors.
      ****/ data binding error ****msg:Identifiers must have user defined types from the XML file. View is missing it</p>
  </blockquote>
  
  <p>Everything compiles (and works!) when I remove the <code>android:visiblity</code> declaration.</p>
  
  <p>I don't see what I'm missing here</p>