image_optim: remove useless nulls

pkgs/applications/graphics/image_optim/default.nix

@@ -1,29 +1,17 @@
 { lib, bundlerApp, bundlerUpdateScript, makeWrapper,
-  withPngcrush ? true,       pngcrush ? null,
-  withPngout ? true,         pngout ? null,
-  withAdvpng ? true,         advancecomp ? null,
-  withOptipng ? true,        optipng ? null,
-  withPngquant ? true,       pngquant ? null,
-  withJhead ? true,          jhead ? null,
-  withJpegoptim ? true,      jpegoptim ? null,
-  withJpegrecompress ? true, jpeg-archive ? null,
-  withJpegtran ? true,       libjpeg ? null,
-  withGifsicle ? true,       gifsicle ? null,
-  withSvgo ? true,           svgo ? null
+  withPngcrush ? true,       pngcrush,
+  withPngout ? true,         pngout,
+  withAdvpng ? true,         advancecomp,
+  withOptipng ? true,        optipng,
+  withPngquant ? true,       pngquant,
+  withJhead ? true,          jhead,
+  withJpegoptim ? true,      jpegoptim,
+  withJpegrecompress ? true, jpeg-archive,
+  withJpegtran ? true,       libjpeg,
+  withGifsicle ? true,       gifsicle,
+  withSvgo ? true,           svgo
 }:
 
-assert withPngcrush       -> pngcrush != null;
-assert withPngout         -> pngout != null;
-assert withAdvpng         -> advancecomp != null;
-assert withOptipng        -> optipng != null;
-assert withPngquant       -> pngquant != null;
-assert withJhead          -> jhead != null;
-assert withJpegoptim      -> jpegoptim != null;
-assert withJpegrecompress -> jpeg-archive != null;
-assert withJpegtran       -> libjpeg != null;
-assert withGifsicle       -> gifsicle != null;
-assert withSvgo           -> svgo != null;
-
 with lib;
 
 let