uiimage blurring: fix error from the future

Sources/UIImage+Blur.m

@@ -26,6 +26,9 @@
 @implementation UIImage (Blur)
 
 + (UIImage *)applyBlurOnImage:(UIImage *)imageToBlur withRadius:(CGFloat)blurRadius {
+    if (!imageToBlur)
+        return NULL;
+
     if ((blurRadius < 0.0f) || (blurRadius > 1.0f)) {
         blurRadius = 0.5f;
     }