Android canvas setMatrix(null) crashes (if preceded by a getMatrix)
<p>In the lunar lander example, if I add the following two lines to the top of the doDraw method, the app crashes immediately with a NullPointerException:</p>

<pre>
Matrix m = canvas.getMatrix();
canvas.setMatrix( null );
</pre>

<p>Stack trace is:</p>

<pre>
FATAL EXCEPTION: Thread-8
java.lang.NullPointerException
    at android.graphics.Matrix.preConcat(Matrix.java:233)
    at android.view.Surface$CompatibleCanvas.setMatrix(Surface.java:259)
    at com.example.android.lunarlander.LunarView$LunarThread.doDraw(LunarView.java:617)
    at com.example.android.lunarlander.LunarView$LunarThread.run(LunarView.java:360)
</pre>

<p>The canvas documentation for setMatrix states that "If the matrix parameter is null, then the current matrix is reset to identity", so there's no reason this should crash.</p>

<p>Also, if I do <b>not</b> call getMatrix before calling setMatrix(null), then setMatrix(null) is <b>successful</b>.  So somehow it is the combination of the two calls that are causing a problem.</p>

<p>Whats going on here?!</p>
