Index: Lib/tarfile.py
===================================================================
--- Lib/tarfile.py	(revision 54888)
+++ Lib/tarfile.py	(revision 54889)
@@ -1044,7 +1044,9 @@
            can be determined, `mode' is overridden by `fileobj's mode.
            `fileobj' is not closed, when TarFile is closed.
         """
-        self.name = os.path.abspath(name)
+        self.name = name
+        if self.name is not None:
+            self.name = os.path.abspath(name)
 
         if len(mode) > 1 or mode not in "raw":
             raise ValueError("mode must be 'r', 'a' or 'w'")