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

builtin/diff.c

@@ -352,7 +352,7 @@ static void symdiff_prepare(struct rev_info *rev, struct symdiff *sym)
 			othercount++;
 			continue;
 		}
-		if (map == NULL)
+		if (!map)
 			map = bitmap_new();
 		bitmap_set(map, i);
 	}