Author: Julia Lawall <julia@diku.dk> find_zlib_workspace returns an ERR_PTR value in an error case instead of NULL. A simplified version of the semantic match that finds this problem is as follows: (http://coccinelle.lip6.fr/) // @match exists@ expression x, E; statement S1, S2; @@ x = find_zlib_workspace(…) … when != x = E ( * if (x == …