SurfaceHolder.lockCanvas () Returns null Even though it was available

I have an Android game on the market and I get NullPointers crash reports when I try to use the canvas. I can assume this because it SurfaceHolder.lockCanvas()returns null, however it does this average gameplay, because depending on where it crashes, it SurfaceHolder.lockCanvas()returned a valid canvas at least once.

This is difficult to debug because I cannot recreate it on my own device, which makes me wonder if this is related to specific devices. The only hint I have is that one of the devices on which this happened was the Nexus 7.

NOTE. This is not the same problem as a question with a similar name. Another question was trying to use the canvas before it was available, while it was available.

Below is a sample of my code:

public class GameView extends SurfaceView implements SurfaceHolder.Callback
{
    class GameThread extends Thread
    {
        @Override
        public void run()
        {
            while (running)
            {
                Canvas c = null;
                try
                {
                    c = mSurfaceHolder.lockCanvas();

                    synchronized (mSurfaceHolder)
                    {
                        long start = System.currentTimeMillis();
                        doDraw(c);
                        long diff = System.currentTimeMillis() - start;

                        if (diff < frameRate)
                            Thread.sleep(frameRate - diff);
                    }
                } catch (InterruptedException e)
                {
                }
                finally
                {
                    if (c != null)
                    {
                        mSurfaceHolder.unlockCanvasAndPost(c);
                    }
                }
            }
        }
    }

    public void surfaceCreated(SurfaceHolder holder)
    {
        if (gThread.getState() == Thread.State.TERMINATED)
        {
            gThread = new GameThread(getHolder(), getContext(), getHandler());
            gThread.start();
        }
        else
        {
            gThread.start();
        }
    }
}