### polar_plot((1/sin(theta)),(theta, pi/12, pi/2))

In Sage notebook v 4.6.1 I wrote:

```
var('theta')
polar_plot((1/sin(theta)),(theta, pi/12, pi/2))
```

I got

```
libpng error: Image width or height is zero in IHDR
Traceback (click to the left of this block for traceback)
...
RuntimeError: Error building image
```

What am I doing wrong?