title: Safe args: cannot resolve symbol 'string'
body: <p>I'm using Navigation Architecture Components, and I wanted to take advantage of the safe args plugin. </p>
  
  <p>I want to add some arguments to one of my fragments in the navigation graph. The arguments code is generated via the Design editor. Here's a snippet:</p>
  
  <pre><code>&lt;fragment
      android:id="@+id/inAppPurchaseFragment"
      android:name="purchaseFragment" &gt;
      &lt;argument
          android:name="attribution_id"
          app:type="string" /&gt;
  &lt;/fragment&gt;
  </code></pre>
  
  <p>However, I'm getting an error in Android Studio (3.2 Canary 16) that says it cannot resolve the symbol 'string', or any type I try to use. Have any of you had this issue &amp; do you know why it's occurring?</p>
  
  <p>Update for more context; I get this error during build on the line that has <code>app:type="string"</code>:</p>
  
  <p><code>error: 'string' is incompatible with attribute type (attr) integer.</code></p>