甲、乙二人系成年人。某日，甲将房屋卖给乙，并签订了房屋买卖合同，乙向甲支付了40万元价款，但甲、乙二人未办理房屋过户手续。不久，甲通过自书遗嘱指定其孙子丙为继承人，继承该房屋。后甲死亡，乙、丙因房屋所有权的归属发生纠纷。经查，甲死亡后除了该房屋外，没有其他财产。
根据上述案情，请回答：

甲所立遗嘱是否有效为什么

1．合同：

售 货 合 同

卖方：

Sellers：GRAPHIC IMAGE. Contract No. : 09SGQ468512

Date： APR. 22, 2009　　　　地址： Signed at: CHANGSHU

Address: 305 SPAGNOH ROAD, NEW YORK USA Telex: 0835

Fax: 83556688

Buyers: CHANGSHU ABC LEATHER GOODS CO. , LTD.

Address: 18, HUANGHE ROAD, CHANGSHU, CHINA. Telex：0512-8657632

Fax: 0512-8657634

This Sales Contract is made by and between the Sellers and the Buyers, whereby the sellers agree to sell and the Buyers agree to buy the under - mentioned goods according to the terms and conditions stipulated below:

(6)Packing: 3QPCS/CARTON (7)Delivery from NEW YORK to CHANGSHU

(8)Time of Shipment: Within (30) days after receipt of L/C. allowing transshipment and partial shipment.

(9)Terms of Payment: By irrevocable Letter of Credit in favor of the Sellers to be available by sight draft to be opened and to reach NEW YORK before MAY 15, 2009 and to remain valied for negotiation in NEW YORK until the 15th days after the foresaid Time of Shipment.

L/C must mention this contract number. All banking Charges outside China(the mainland of China) are for account of the Beneficiary

(10)Insurance：To be effected by Sellers for 110% of full invoice value coveting F.P.A. up to CHANGSHU

(11)Arbitration: All dispute arising from be execuion of or in connection with this contract shall be settled amizedly by negotiation. In ease of settlement can not be reached through negotiation the case shall then be submit China international Economic & Trade Arbitration Commision. In Nanjing (or in Beijing) for arbitration in act with its sure of procedures. The arbitral award is final and binding upon both parties.

The Seller GRAPHIC IMAGE. The Buyer CHANGSHU ABC LEATHER GOODS CO. , LTD.

2．其他资料：

申请开证日期：2009年4月26日

二、根据已知资料用英文缮制开证申请书

TO:　　　　　　　　　　　　　　　 Date: