NPE while capturer.captureScreenshot() call

```java 
	public void evaluate() throws Throwable {
		FrameworkMethod before = null;
		try {
			for (FrameworkMethod bfr : fBefores) {
				before = bfr;
				before.invokeExplosively(fTarget);
			}
		} catch (Throwable throwable) {
			CaptureScreenshot capturer = new CaptureScreenshot();
			capturer.captureScreenshot(fTarget.getClass().getCanonicalName() + "-" + before.getName());
			throw throwable;
		}
		fNext.evaluate();
	}
```