kustomize transformers to create fields if they are null

api/filters/namespace/namespace.go

@@ -44,6 +44,7 @@ func (ns Filter) run(node *yaml.RNode) (*yaml.RNode, error) {
 		FsSlice:    ns.FsSlice,
 		SetValue:   fsslice.SetScalar(ns.Namespace),
 		CreateKind: yaml.ScalarNode, // Namespace is a ScalarNode
+		CreateTag:  yaml.StringTag,
 	})
 	return node, err
 }

api/filters/namespace/namespace_test.go

@@ -44,6 +44,37 @@ metadata:
 		filter: namespace.Filter{Namespace: "foo"},
 	},
 
+	{
+		name: "null_ns",
+		input: `
+apiVersion: example.com/v1
+kind: Foo
+metadata:
+  name: instance
+  namespace: null
+---
+apiVersion: example.com/v1
+kind: Bar
+metadata:
+  name: instance
+  namespace: null
+`,
+		expected: `
+apiVersion: example.com/v1
+kind: Foo
+metadata:
+  name: instance
+  namespace: foo
+---
+apiVersion: example.com/v1
+kind: Bar
+metadata:
+  name: instance
+  namespace: foo
+`,
+		filter: namespace.Filter{Namespace: "foo"},
+	},
+
 	{
 		name: "add-recurse",
 		input: `