commit 0416d6f05a96e0f1b3751aa97abfffe6d3323976
author Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> Wed May 22 18:41:43 2019 -0700
committer R. David Murray <rdmurray@bitdance.com> Wed May 22 21:41:43 2019 -0400
tree 14274d5ee030e346445be5dcaf74450c7d430563
parent 367fe5757a707c4e3602dee807a9315199ed0b5c

bpo-27737: Allow whitespace only headers encoding (GH-13478) (#13517)

(cherry picked from commit ef5bb25e2d6147cd44be9c9b166525fb30485be0)

Co-authored-by: Batuhan Taşkaya <47358913+isidentical@users.noreply.github.com>

Lib/email/header.py

diff --git a/Lib/email/header.py b/Lib/email/header.py
index 7b30a03..4ab0032 100644
--- a/Lib/email/header.py
+++ b/Lib/email/header.py
@@ -431,7 +431,7 @@
         if end_of_line != (' ', ''):
             self._current_line.push(*end_of_line)
         if len(self._current_line) > 0:
-            if self._current_line.is_onlyws():
+            if self._current_line.is_onlyws() and self._lines:
                 self._lines[-1] += str(self._current_line)
             else:
                 self._lines.append(str(self._current_line))