implement use case when null is set

conflate_test.go

@@ -21,6 +21,11 @@ type TestData struct {
 	All           string `json:"all"`
 }
 
+type TestNulledData struct {
+	Foo string `yaml:"foo"`
+	Bar string `yaml:"bar"`
+}
+
 func TestFromFiles(t *testing.T) {
 	c, err := FromFiles("testdata/valid_parent.json")
 	assert.Nil(t, err)
@@ -361,3 +366,14 @@ func TestConflate_mergeDataError(t *testing.T) {
 	assert.NotNil(t, err)
 	assert.Contains(t, err.Error(), "failed to merge")
 }
+
+func TestFromFilesNulled(t *testing.T) {
+	c, err := FromFiles("testdata/test_not_nulled.yaml", "testdata/test_nulled.yaml")
+	assert.Nil(t, err)
+	assert.NotNil(t, c)
+	var testData TestNulledData
+	err = c.Unmarshal(&testData)
+	assert.Nil(t, err)
+	assert.Equal(t, "foo", testData.Foo)
+	assert.Equal(t, "", testData.Bar)
+}

merge.go

@@ -84,6 +84,11 @@ func mergeMapRecursive(ctx context, toData, fromData interface{}) error {
 	}
 
 	for name, fromProp := range fromProps {
+		// merge in explicit nil values
+		if fromProp == nil {
+			toProps[name] = nil
+			continue
+		}
 		if val := toProps[name]; val == nil {
 			toProps[name] = fromProp
 		} else {

testdata/test_not_nulled.yaml

@@ -0,0 +1,2 @@
+foo: foo
+bar: bar

testdata/test_nulled.yaml

@@ -0,0 +1,2 @@
+foo: foo
+bar: null