Binary field tree view causes error on empty field

This bug occurs when you add a binary field on a tree view. When you do, and the field is empty, it still provides you with a download-button, as well as file information regarding the non-existing file (it states that the file is 0.00 bytes).

When pressing the "download" button when the field itself is empty, the server presents you with an error, namely:
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Internal Server Error

{"message": "OpenERP WebClient Error", "code": 300, "data": {"debug": "Client Traceback (most recent call last):\n File \"/$mylocation/web/http.py\", line 284, in dispatch\n r = method(self, **self.params)\n File \"/$mylocation/web/controllers/main.py\", line 1282, in saveas\n filecontent = base64.b64decode(res.get(field, ''))\n File \"/usr/lib/python2.6/base64.py\", line 73, in b64decode\n return binascii.a2b_base64(s)\nTypeError: a2b_base64() argument 1 must be string or read-only character buffer, not bool\n", "type": "client_exception"}}
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The form view does this correctly, by not displaying a button nor file information.

Using OpenERP v7 from the /7 branch.
Server revno: 4910
Addons revno: 8950
Web revno: 3867