ble. Instead, claims of privilege must be made on a document-by-document basis. United States v. Davis, 636 F.2d 1028, 1038 (5th Cir. 1981);9 In re Grand Juty Subpoena, 831 F.2d 225, 227 (11th Cir. 1987). A blanket assertion cannot be used to avoid testifying; instead, a witness' claims of attorney-client privileg