fix: empty map to empty json (#38)

Co-authored-by: mrekhi <mandeep.rekhi@nokia.com>
Co-authored-by: Michael Weibel <307427+mweibel@users.noreply.github.com>

sheriff.go

@@ -248,7 +248,7 @@ func marshalValue(options *Options, v reflect.Value) (interface{}, error) {
 	if k == reflect.Map {
 		mapKeys := v.MapKeys()
 		if len(mapKeys) == 0 {
-			return nil, nil
+			return val, nil
 		}
 		if mapKeys[0].Kind() != reflect.String {
 			return nil, MarshalInvalidTypeError{t: mapKeys[0].Kind(), data: val}

sheriff_test.go

@@ -505,13 +505,33 @@ func TestMarshal_EmptyMap(t *testing.T) {
 	assert.NoError(t, err)
 
 	expected, err := json.Marshal(map[string]interface{}{
-		"a_map": nil,
+		"a_map": make(map[string]interface{}),
 	})
 	assert.NoError(t, err)
 
 	assert.Equal(t, string(expected), string(actual))
 }
 
+func TestMarshal_EmptyMapJson(t *testing.T) {
+	emp := EmptyMapTest{
+		AMap: make(map[string]string),
+	}
+	o := &Options{
+		Groups: []string{"test"},
+	}
+
+	actualMap, err := Marshal(o, emp)
+	assert.NoError(t, err)
+
+	actual, err := json.Marshal(actualMap)
+	assert.NoError(t, err)
+
+	expected, err := json.Marshal(emp)
+	assert.NoError(t, err)
+
+	assert.Equal(t, string(expected), string(actual))
+}
+
 type TestMarshal_Embedded struct {
 	Foo string `json:"foo" groups:"test"`
 }