How can I specify a null as an XML attribute for Android?
<p>What do I need to put in for an attribute if I want to put a null there?</p>

<p>For example, this piece of code:</p>

<pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;transition xmlns:android="http://schemas.android.com/apk/res/android" &gt;

    &lt;item android:drawable="@drawable/ef_gradient_blue" /&gt;
    &lt;item android:drawable="@null" /&gt;

&lt;/transition&gt;
</code></pre>

<p>But this won't work, as my app crashes when it tries to load this drawable. I need it to be null, so it can make a transition from fully opaque to completely see through.</p>

<p>In my Java, I load it like this:</p>

<pre><code>mTransitionBlue = (TransitionDrawable)mProjectResources.getDrawable(R.drawable.transition_blue);
</code></pre>

<p>But I get a runtime exception from this, saying it can't find the transition_blue.xml, which is the XML specified before. So how do I achieve this?</p>
