add SetKeepNilAsNull to set null values

README.md

@@ -39,6 +39,12 @@ Sets `value` on `data` at that json path
 
 Note: you'll want to pass in a pointer to `data` so that the side effect actually is usable
 
+### jsonpath.SetKeepNilAsNull(data interface{}, path string, value interface{}) (error)
+
+Sets `value` on `data` at that json path while translating `nil` values as `null` instead of removing the key.
+
+Note: you'll want to pass in a pointer to `data` so that the side effect actually is usable
+
 ### jsonpath.DoesNotExist error
 
 Returned by  `jsonpath.Get` on a nonexistent path:

jsonpath.go

@@ -107,8 +107,16 @@ func Get(data interface{}, path string) (interface{}, error) {
 	return getByTokens(data, tokens)
 }
 
-// Set value on data at that json path
 func Set(data interface{}, path string, value interface{}) error {
+	return set(data, path, value, false)
+}
+
+func SetKeepNilAsNull(data interface{}, path string, value interface{}) error {
+	return set(data, path, value, true)
+}
+
+// Set value on data at that json path
+func set(data interface{}, path string, value interface{}, keepNilAsNull bool) error {
 	tokens, err := tokenizePath(path)
 	if err != nil {
 		return nil
@@ -118,7 +126,9 @@ func Set(data interface{}, path string, value interface{}) error {
 	last := tokens[len(tokens)-1]
 
 	data = followPtr(data)
-	value = followPtr(value)
+	if value != nil {
+		value = followPtr(value)
+	}
 
 	child := data
 	parent := data
@@ -163,7 +173,12 @@ func Set(data interface{}, path string, value interface{}) error {
 
 	switch reflect.ValueOf(child).Kind() {
 	case reflect.Map:
-		reflect.ValueOf(child).SetMapIndex(reflect.ValueOf(last), reflect.ValueOf(value))
+		if value == nil && keepNilAsNull {
+			var nilvalue interface{}
+			reflect.ValueOf(child).SetMapIndex(reflect.ValueOf(last), reflect.ValueOf(&nilvalue).Elem())
+		} else {
+			reflect.ValueOf(child).SetMapIndex(reflect.ValueOf(last), reflect.ValueOf(value))
+		}
 		return nil
 	case reflect.Slice:
 		sliceValue := reflect.ValueOf(child)

jsonpath_test.go

@@ -109,10 +109,10 @@ func TestJSON(t *testing.T) {
 	"pet": {
 		"name": "baxter",
 		"owner": {
-      "name": "john doe",
-      "contact": {
-			  "phone": "859-289-9290"
-      }
+		"name": "john doe",
+			"contact": {
+				"phone": "859-289-9290"
+			}
 		},
 		"type": "dog",
     "age": "4"
@@ -192,3 +192,37 @@ func TestErrors(t *testing.T) {
 		t.Errorf("error retrieving value %v", err)
 	}
 }
+
+func TestNullRemovesKey(t *testing.T) {
+	var payload = map[string]interface{}{
+		"key1": "val1",
+	}
+	err := Set(&payload, "key1", nil)
+	if err != nil {
+		t.Error("error setting a nil value failed", err)
+	}
+
+	_, ok := payload["key1"]
+	if ok {
+		t.Error("nil values assigned with Set should remove the key", err)
+	}
+}
+
+func TestNullSetWithSetKeepNilAsNullKeepKey(t *testing.T) {
+	var payload = map[string]interface{}{
+		"key1": "val1",
+	}
+
+	err := SetKeepNilAsNull(&payload, "key1", nil)
+	if err != nil {
+		t.Error("error setting a nil value failed", err)
+	}
+
+	val, ok := payload["key1"]
+	if !ok {
+		t.Error("nil values assigned with SetKeepNilAsNull should keep the key", err)
+	}
+	if val != nil {
+		t.Error("nil values assigned with SetKeepNilAsNull should set the key to null", err)
+	}
+}