fix: Invalid result of Reddit query

When Reddit cannot find query, it should return empty list.

reddit.go

@@ -23,6 +23,19 @@ type RedditResponse struct {
 	} `json:"data"`
 }
 
+// UnmarshalJSON deserialize inconsistent JSON responses to RedditResponse.
+// Reddit returns empty object ("{}") when there are no search results.
+func (r *RedditResponse) UnmarshalJSON(b []byte) error {
+	isEmptyResponse := len(b) == 4 && string(b) == "\"{}\""
+	if isEmptyResponse {
+		return nil
+	}
+
+	// new type prevents recursive calls to RedditResponse.UnmarshalJSON()
+	type resp *RedditResponse
+	return json.Unmarshal(b, resp(r))
+}
+
 // SearchReddit searches Reddit for given query and returns list of discussions
 // sorted by relevance.
 //

reddit_test.go

@@ -18,3 +18,14 @@ func ExampleSearchReddit() {
 	// Output:
 	// Reddit	https://reddit.com/r/hypeurls/comments/17k6i1l/the_grug_brained_developer_2022/	The Grug Brained Developer (2022)	https://grugbrain.dev/
 }
+
+func ExampleSearchReddit_unknown() {
+	client := http.Client{}
+	query := "https://invalid.domain/query"
+
+	opinions := ensure.MustReturn(SearchReddit(context.TODO(), client, query))
+
+	fmt.Println(len(opinions))
+	// Output:
+	// 0
+}