fixed wrong comparison of nullable values

src/VahterBanBot/DB.fs

@@ -21,22 +21,26 @@ VALUES (@id, @username, @banReason, @bannedAt, @bannedBy, @createdAt, @updatedAt
 ON CONFLICT (id) DO UPDATE
     SET username   =
             CASE
-                WHEN EXCLUDED.username != "user".username THEN COALESCE(EXCLUDED.username, "user".username) 
+                WHEN EXCLUDED.username IS DISTINCT FROM "user".username
+                    THEN COALESCE(EXCLUDED.username, "user".username)
                 ELSE "user".username
                 END,
         ban_reason =
             CASE
-                WHEN EXCLUDED.ban_reason != "user".ban_reason THEN COALESCE(EXCLUDED.ban_reason, "user".ban_reason)
+                WHEN EXCLUDED.ban_reason IS DISTINCT FROM "user".ban_reason
+                    THEN COALESCE(EXCLUDED.ban_reason, "user".ban_reason)
                 ELSE "user".ban_reason
                 END,
-        banned_at = 
+        banned_at  =
             CASE
-                WHEN EXCLUDED.banned_at != "user".banned_at THEN COALESCE(EXCLUDED.banned_at, "user".banned_at)
+                WHEN EXCLUDED.banned_at IS DISTINCT FROM "user".banned_at
+                    THEN COALESCE(EXCLUDED.banned_at, "user".banned_at)
                 ELSE "user".banned_at
                 END,
-        banned_by =
+        banned_by  =
             CASE
-                WHEN EXCLUDED.banned_by != "user".banned_by THEN COALESCE(EXCLUDED.banned_by, "user".banned_by)
+                WHEN EXCLUDED.banned_by IS DISTINCT FROM "user".banned_by
+                    THEN COALESCE(EXCLUDED.banned_by, "user".banned_by)
                 ELSE "user".banned_by
                 END,
         updated_at = GREATEST(EXCLUDED.updated_at, "user".updated_at)