kustomize transformers to create fields if they are null

api/filters/labels/labels.go

@@ -33,6 +33,7 @@ func (f Filter) Filter(nodes []*yaml.RNode) ([]*yaml.RNode, error) {
 					FsSlice:    f.FsSlice,
 					SetValue:   fsslice.SetEntry(k, f.Labels[k], yaml.StringTag),
 					CreateKind: yaml.MappingNode, // Labels are MappingNodes.
+					CreateTag:  "!!map",
 				}); err != nil {
 					return nil, err
 				}

api/filters/labels/labels_test.go

@@ -370,6 +370,35 @@ metadata:
 				},
 			},
 		},
+
+		"null_labels": {
+			input: `
+apiVersion: example.com/v1
+kind: Foo
+metadata:
+  name: instance
+  labels: null
+`,
+			expectedOutput: `
+apiVersion: example.com/v1
+kind: Foo
+metadata:
+  name: instance
+  labels:
+    a: a1
+`,
+			filter: Filter{
+				Labels: labelMap{
+					"a": "a1",
+				},
+				FsSlice: []types.FieldSpec{
+					{
+						Path:               "metadata/labels",
+						CreateIfNotPresent: true,
+					},
+				},
+			},
+		},
 	}
 
 	for tn, tc := range testCases {