s:NULL backend:None backend:

bin/varnishtest/tests/d00030.vtc

@@ -185,7 +185,7 @@ varnish v1 -errvcl {vmod_directors: shard shard: .backend(resolve=NOW) can not b
     }
 }
 
-varnish v1 -errvcl {vmod_directors: shard shard: NULL backend cannot be added}{
+varnish v1 -errvcl {vmod_directors: shard shard: None backend cannot be added}{
     import directors;
 
     backend dummy None;

bin/varnishtest/tests/r02036.vtc

@@ -7,7 +7,7 @@ server s1 {
 
 varnish v1 -vcl+backend {} -start
 
-varnish v1 -errvcl "NULL backend cannot be added" {
+varnish v1 -errvcl "None backend cannot be added" {
 	import directors;
 
 	probe cacheprobe {

bin/varnishtest/tests/v00060.vtc

-varnishtest "NULL backend allowed"
+varnishtest "None backend allowed"
 
 server s1 {
 	rxreq

vmod/vmod_directors.c

@@ -137,7 +137,7 @@ vdir_add_backend(VRT_CTX, struct vdir *vd, VCL_BACKEND be, double weight)
 	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
 	CHECK_OBJ_NOTNULL(vd, VDIR_MAGIC);
 	if (be == NULL) {
-		VRT_fail(ctx, "%s: NULL backend cannot be added",
+		VRT_fail(ctx, "%s: None backend cannot be added",
 		    VRT_BACKEND_string(vd->dir));
 		return;
 	}
@@ -160,7 +160,7 @@ vdir_remove_backend(VRT_CTX, struct vdir *vd, VCL_BACKEND be, unsigned *cur)
 	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
 	CHECK_OBJ_NOTNULL(vd, VDIR_MAGIC);
 	if (be == NULL) {
-		VRT_fail(ctx, "%s: NULL backend cannot be removed",
+		VRT_fail(ctx, "%s: None backend cannot be removed",
 		    VRT_BACKEND_string(vd->dir));
 		return;
 	}

vmod/vmod_directors_shard.c

@@ -319,7 +319,7 @@ vmod_shard_add_backend(VRT_CTX, struct vmod_directors_shard *vshard,
 
 	if (args->backend == NULL) {
 		shard_fail(ctx, vshard->shardd->name, "%s",
-		    "NULL backend cannot be added");
+		    "None backend cannot be added");
 		return (0);
 	}