Update

frontend/src/components/EpisodeList.tsx

@@ -165,14 +165,18 @@ function EpisodeList() {
   };
 
   const filterEpisodesByCategory = async () => {
-    const response = await fetch(
-      `/api/episodes/by-category?category=${selectedCategory}`,
-    );
-    const episodes = await response.json();
-
     if (!selectedCategory) {
       setFilteredEpisodes(episodes);
     } else {
+      const response = await fetch(
+        `/api/episodes/by-category?category=${selectedCategory}`,
+      );
+      if (!response.ok) {
+        setError("カテゴリの取得に失敗しました");
+        return;
+      }
+      const episodes = await response.json();
+
       setFilteredEpisodes(episodes);
     }
   };