Creating a Slick image with no texture should not be possible; it will likely throw a null pointer since Texture is expected to be non-null.
For offscreen buffers where you plan to use getGraphics, you should use the new Image.createOffscreenImage utility and specify a filter there.
I don't understand why you don't just use non-power-of-two tiles, e.g. 45x45.
P.S. In future, always post the exception.
Non power of two tiles don't fit quite as well on my sprite sheets... Well, that WOULD solve my problem, but let me play the devil's advocate for a moment. What would be the best course of action if I wanted my game's camera to zoom in and out occasionally?
Edit: Before I forget, I would like to point out that I've never been able to download a copy of slick that has the method createOffscreenImage() located in the Image class. Am I perhaps downloading the incorrect distribution? I always try to find the latest, but I can't seem to find one with that method. I only every see it in examples.