bindings/python-cffi: fix docstring for message.header()

The cffi bindings raise a LookupError in case a header is not present.
Adjust the docstring to say so.

The legacy bindings behaved differently, and this is one of the things
to be aware of when migrating to the cffi bindings.

diff --git a/bindings/python-cffi/notmuch2/_message.py b/bindings/python-cffi/notmuch2/_message.py
index f4c7ef0217032fa0d27a64a5718faa305de60519..7bd2033121bfd4701af9066d041459735bd7754d 100644 (file)
--- a/bindings/python-cffi/notmuch2/_message.py
+++ b/bindings/python-cffi/notmuch2/_message.py
@@ -240,8 +240,7 @@ class Message(base.NotmuchObject):
         :param header: Case-insensitive header name to retrieve.
         :type header: str or bytes
 
-        :returns: The header value, an empty string if the header is
-           not present.
+        :returns: The header value.
         :rtype: str
 
         :raises LookupError: if the header is not present.