fix(utils): fixes #162

internal/utils/diff_map.go

@@ -216,6 +216,13 @@ func addSliceDiff(newSlice reflect.Value, existingSlice reflect.Value, jsonTag s
 	if err != nil {
 		return fmt.Errorf("error converting slice to comparable slice: %s", err)
 	}
+
+	// If second slice is empty or not valid set new
+	if !existingSlice.IsValid() || existingSlice.Len() == 0 {
+		diffMap[jsonTag] = newSlice.Interface()
+		return nil
+	}
+
 	existingSlice, err = convertSliceToComparableSlice(existingSlice)
 	if err != nil {
 		return fmt.Errorf("error converting slice to comparable slice: %s", err)

internal/utils/diff_map_test.go

@@ -921,6 +921,30 @@ func Test_addSliceDiff(t *testing.T) {
 			wantErr:     false,
 			wantDiffMap: map[string]interface{}{"test": []int{1, 2}},
 		},
+		{
+			name: "Has priority. Existing slice is nil",
+			args: args{
+				newSlice:      reflect.ValueOf([]testStructWithIntIDAttribute{{ID: 1}, {ID: 2}}),
+				existingSlice: reflect.ValueOf(nil),
+				jsonTag:       "test",
+				hasPriority:   true,
+				diffMap:       map[string]interface{}{},
+			},
+			wantErr:     false,
+			wantDiffMap: map[string]interface{}{"test": []int{1, 2}},
+		},
+		{
+			name: "Has priority. Same Existing slice is empty",
+			args: args{
+				newSlice:      reflect.ValueOf([]testStructWithIntIDAttribute{{ID: 1}, {ID: 2}}),
+				existingSlice: reflect.ValueOf([]testStructWithIntIDAttribute{}),
+				jsonTag:       "test",
+				hasPriority:   true,
+				diffMap:       map[string]interface{}{},
+			},
+			wantErr:     false,
+			wantDiffMap: map[string]interface{}{"test": []int{1, 2}},
+		},
 		{
 			name: "Has priority. Same length and the same. Slice with structs with ID attributes.",
 			args: args{