Preserve null values when converting nil containers to JSON

conversions.go

@@ -60,6 +60,9 @@ func (m Map) JSON() (string, error) {
 }
 
 func cleanUpInterfaceArray(in []interface{}) []interface{} {
+	if in == nil {
+		return nil
+	}
 	result := make([]interface{}, len(in))
 	for i, v := range in {
 		result[i] = cleanUp(v)
@@ -68,6 +71,9 @@ func cleanUpInterfaceArray(in []interface{}) []interface{} {
 }
 
 func cleanUpInterfaceMap(in map[interface{}]interface{}) Map {
+	if in == nil {
+		return nil
+	}
 	result := Map{}
 	for k, v := range in {
 		result[fmt.Sprintf("%v", k)] = cleanUp(v)
@@ -76,6 +82,9 @@ func cleanUpInterfaceMap(in map[interface{}]interface{}) Map {
 }
 
 func cleanUpStringMap(in map[string]interface{}) Map {
+	if in == nil {
+		return nil
+	}
 	result := Map{}
 	for k, v := range in {
 		result[k] = cleanUp(v)
@@ -84,6 +93,9 @@ func cleanUpStringMap(in map[string]interface{}) Map {
 }
 
 func cleanUpMSIArray(in []map[string]interface{}) []Map {
+	if in == nil {
+		return nil
+	}
 	result := make([]Map, len(in))
 	for i, v := range in {
 		result[i] = cleanUpStringMap(v)
@@ -92,6 +104,9 @@ func cleanUpMSIArray(in []map[string]interface{}) []Map {
 }
 
 func cleanUpMapArray(in []Map) []Map {
+	if in == nil {
+		return nil
+	}
 	result := make([]Map, len(in))
 	for i, v := range in {
 		result[i] = cleanUpStringMap(v)

conversions_nil_test.go

@@ -0,0 +1,62 @@
+package objx_test
+
+import (
+	"encoding/base64"
+	"testing"
+
+	"github.com/stretchr/objx"
+)
+
+func TestConversionJSONPreservesNilContainers(t *testing.T) {
+	tests := []struct {
+		name  string
+		value interface{}
+		json  string
+	}{
+		{"nil interface slice", []interface{}(nil), "null"},
+		{"nil map slice", []objx.Map(nil), "null"},
+		{"nil string map slice", []map[string]interface{}(nil), "null"},
+		{"nil map", objx.Map(nil), "null"},
+		{"nil interface map", map[interface{}]interface{}(nil), "null"},
+		{"nil string map", map[string]interface{}(nil), "null"},
+		{"nil string slice", []string(nil), "null"},
+		{"nil interface", nil, "null"},
+		{"empty interface slice", []interface{}{}, "[]"},
+		{"empty map slice", []objx.Map{}, "[]"},
+		{"empty string map slice", []map[string]interface{}{}, "[]"},
+		{"empty map", objx.Map{}, "{}"},
+		{"empty interface map", map[interface{}]interface{}{}, "{}"},
+		{"populated interface slice", []interface{}{1}, "[1]"},
+		{"populated map slice", []objx.Map{{"key": "value"}}, `[{"key":"value"}]`},
+		{"populated string map slice", []map[string]interface{}{{"key": "value"}}, `[{"key":"value"}]`},
+		{"populated map", objx.Map{"key": "value"}, `{"key":"value"}`},
+		{"populated interface map", map[interface{}]interface{}{1: "value"}, `{"1":"value"}`},
+	}
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			for _, context := range []struct {
+				name  string
+				input objx.Map
+				want  string
+			}{
+				{"direct", objx.Map{"value": test.value}, `{"value":` + test.json + `}`},
+				{"in slice", objx.Map{"value": []interface{}{test.value}}, `{"value":[` + test.json + `]}`},
+				{"in map", objx.Map{"value": objx.Map{"nested": test.value}}, `{"value":{"nested":` + test.json + `}}`},
+			} {
+				t.Run(context.name, func(t *testing.T) {
+					got, err := context.input.JSON()
+					require.NoError(t, err)
+					assert.Equal(t, context.want, got)
+					assert.Equal(t, context.want, context.input.MustJSON())
+					encoded, err := context.input.Base64()
+					require.NoError(t, err)
+					decoded, err := base64.StdEncoding.DecodeString(encoded)
+					require.NoError(t, err)
+					assert.Equal(t, context.want, string(decoded))
+				})
+			}
+		})
+	}
+}