remove unnecessary NULL check before free(3)

free(3) handles NULL pointers just fine.  Add a semantic patch for
removing unnecessary NULL checks before calling this function, and
apply it on the code base.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/coccinelle/free.cocci

@@ -0,0 +1,5 @@
+@@
+expression E;
+@@
+- if (E)
+  free(E);

parse-options-cb.c

@@ -199,8 +199,7 @@ int parse_opt_passthru(const struct option *opt, const char *arg, int unset)
 	if (recreate_opt(&sb, opt, arg, unset) < 0)
 		return -1;
 
-	if (*opt_value)
-		free(*opt_value);
+	free(*opt_value);
 
 	*opt_value = strbuf_detach(&sb, NULL);