Revert "fix: empty map to empty json (#38)"

This reverts commit 8d57885.

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 val, nil
+			return nil, nil
 		}
 		if mapKeys[0].Kind() != reflect.String {
 			return nil, MarshalInvalidTypeError{t: mapKeys[0].Kind(), data: val}

sheriff_test.go

@@ -505,33 +505,13 @@ func TestMarshal_EmptyMap(t *testing.T) {
 	assert.NoError(t, err)
 
 	expected, err := json.Marshal(map[string]interface{}{
-		"a_map": make(map[string]interface{}),
+		"a_map": nil,
 	})
 	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"`
 }