Merge branch 'ep/maint-equals-null-cocci'

Introduce and apply coccinelle rule to discourage an explicit
comparison between a pointer and NULL, and applies the clean-up to
the maintenance track.

* ep/maint-equals-null-cocci:
  tree-wide: apply equals-null.cocci
  tree-wide: apply equals-null.cocci
  contrib/coccinnelle: add equals-null.cocci

refs/ref-cache.c

@@ -134,7 +134,7 @@ int search_ref_dir(struct ref_dir *dir, const char *refname, size_t len)
 	r = bsearch(&key, dir->entries, dir->nr, sizeof(*dir->entries),
 		    ref_entry_cmp_sslice);
 
-	if (r == NULL)
+	if (!r)
 		return -1;
 
 	return r - dir->entries;