Problem reported upstream:
https://github.com/linsomniac/python-memcached/issues/176

---
 memcache.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/memcache.py b/memcache.py
index 05b6657..b935681 100644
--- a/memcache.py
+++ b/memcache.py
@@ -1300,8 +1300,8 @@ class Client(threading.local):
             key = key[1]
         if key is None:
             raise Client.MemcachedKeyNoneError("Key is None")
-        if key is '':
-            if key_extra_len is 0:
+        if key == '':
+            if key_extra_len == 0:
                 raise Client.MemcachedKeyNoneError("Key is empty")

             #  key is empty but there is some other component to key
--
2.26.2
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<tr><td><span title='2019-02-04 00:03:30 +0100'>2019-02-04</span></td><td><a href='/guix/commit/build-aux/test-env.in?id=a87d66f371da2a84d7bba1cae58b71c9c9af73aa'>daemon: Rename 'NIX_STATE_DIR' and 'NIX_DB_DIR' environment variables.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/22459&gt;.
Reported by Jeff Mickey &lt;j@codemac.net&gt;.

* guix/config.scm.in (%state-directory): Change NIX_STATE_DIR to
GUIX_STATE_DIRECTORY.
(%store-database-directory): Change NIX_DB_DIR to
GUIX_DATABASE_DIRECTORY.
* nix/libstore/globals.cc (Settings::processEnvironment): Likewise.
* guix/self.scm (make-config.scm): Likewise.
* build-aux/build-self.scm (make-config.scm): Likewise.
* build-aux/test-env.in: Likewise.
* tests/derivations.scm ("derivation #:leaked-env-vars"): Likewise.
* tests/guix-build.sh (GUIX_DAEMON_SOCKET): Likewise.
* tests/guix-daemon.sh (socket): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>