Fix mod flatten including non-existent arrays

gjson.go

@@ -2176,11 +2176,6 @@ func parseAny(json string, i int, hit bool) (int, Result, bool) {
 	return i, res, false
 }
 
-var ( // used for testing
-	testWatchForFallback bool
-	testLastWasFallback  bool
-)
-
 // GetMany searches json for the multiple paths.
 // The return value is a Result array where the number of items
 // will be equal to the number of input paths.
@@ -2745,19 +2740,24 @@ func modFlatten(json, arg string) string {
 	out = append(out, '[')
 	var idx int
 	res.ForEach(func(_, value Result) bool {
+		var raw string
+		if value.IsArray() {
+			if deep {
+				raw = unwrap(modFlatten(value.Raw, arg))
+			} else {
+				raw = unwrap(value.Raw)
+			}
+		} else {
+			raw = value.Raw
+		}
+		raw = strings.TrimSpace(raw)
+		if len(raw) > 0 {
 			if idx > 0 {
 				out = append(out, ',')
 			}
-		if value.IsArray() {
-			if deep {
-				out = append(out, unwrap(modFlatten(value.Raw, arg))...)
-			} else {
-				out = append(out, unwrap(value.Raw)...)
-			}
-		} else {
-			out = append(out, value.Raw...)
-		}
+			out = append(out, raw...)
 			idx++
+		}
 		return true
 	})
 	out = append(out, ']')

gjson_test.go

@@ -787,6 +787,12 @@ var manyJSON = `  {
 func combine(results []Result) string {
 	return fmt.Sprintf("%v", results)
 }
+
+var ( // used for testing
+	testWatchForFallback bool
+	testLastWasFallback  bool
+)
+
 func TestManyBasic(t *testing.T) {
 	testWatchForFallback = true
 	defer func() {
@@ -2222,3 +2228,8 @@ func TestSubpathsWithMultipaths(t *testing.T) {
 	assert(t, Get(json, `#.@ugly`).Raw == `[{"a":1},{"a":2,"values":["a","b","c","d","e"]},true,["a","b","c","d","e"],4]`)
 	assert(t, Get(json, `#.[0,3]`).Raw == `[[],[],[],["a","d"],[]]`)
 }
+
+func TestFlattenRemoveNonExist(t *testing.T) {
+	raw := Get("[[1],[2,[[],[3]],[4,[5],[],[[[6]]]]]]", `@flatten:{"deep":true}`).Raw
+	assert(t, raw == "[1,2,3,4,5,6]")
+}