fix(jsonfeed): avoid panic when parsing null JSON feed

internal/reader/json/parser.go

@@ -14,7 +14,7 @@ import (
 // Parse returns a normalized feed struct from a JSON feed.
 func Parse(baseURL string, data io.Reader) (*model.Feed, error) {
 	jsonFeed := new(JSONFeed)
-	if err := json.NewDecoder(data).Decode(&jsonFeed); err != nil {
+	if err := json.NewDecoder(data).Decode(jsonFeed); err != nil {
 		return nil, fmt.Errorf("json: unable to parse feed: %w", err)
 	}
 

internal/reader/json/parser_test.go

@@ -1012,3 +1012,15 @@ func TestParseInvalidJSON(t *testing.T) {
 		t.Error("Parse should returns an error")
 	}
 }
+
+func TestParseNullJSONFeed(t *testing.T) {
+	data := `null`
+	feed, err := Parse("https://example.org/feed.json", bytes.NewBufferString(data))
+	if err != nil {
+		t.Fatalf("Unexpected error when parsing null feed: %v", err)
+	}
+
+	if feed == nil {
+		t.Fatalf("Feed should not be nil")
+	}
+}