diff --git a/daos/response.php b/daos/response.php
index 1d9aa6d..921401a 100644
--- a/daos/response.php
+++ b/daos/response.php
@@ -8,8 +8,8 @@ Response
 {
   public static function
   fetch_all (
-      SQLite3 $db,
-      int     $thread_id)
+      \SQLite3  $db,
+      int       $thread_id)
   : array
   {
     $sql = "
@@ -59,7 +59,7 @@ Response
 
   public static function
   like (
-      SQLite3 $db,
+      \SQLite3 $db,
       int     $thread_id,
       int     $response_id)
   : void
@@ -79,7 +79,7 @@ Response
 
   public static function
   dislike (
-      SQLite3 $db,
+      \SQLite3 $db,
       int     $thread_id,
       int     $response_id)
   : void
diff --git a/daos/thread.php b/daos/thread.php
index 9f7ecb7..9cd44f9 100644
--- a/daos/thread.php
+++ b/daos/thread.php
@@ -8,7 +8,7 @@ Thread
 {
   public static function
   fetch_all (
-      SQLite3 $db)
+      \SQLite3  $db)
   : array
   {
     $sql = "
@@ -53,8 +53,8 @@ Thread
 
   public static function
   find (
-      SQLite3 $db,
-      int     $id)
+      \SQLite3  $db,
+      int       $id)
   : ?\Dto\Thread
   {
     $sql = "
@@ -77,6 +77,10 @@ Thread
           latest DESC";
 
     $result = $db -> query ($sql);
+
+    if ($row === false)
+      return null;
+
     $row = $result -> fetchArray (SQLITE3_ASSOC);
 
     if ($row === false)
@@ -95,9 +99,9 @@ Thread
 
   public static function
   create_thread (
-      SQLite3 $db,
-      string  $title,
-      string  $explain)
+      \SQLite3  $db,
+      string    $title,
+      string    $explain)
   : void
   {
     ;
@@ -106,7 +110,7 @@ Thread
 
   public static function
   delete_thread (
-      SQLite3 $db,
+      \SQLite3 $db,
       int     $id)
   : void
   {