[pgp] handle case when some of enumerated keys have no non-empty uids

pgp/backend/python_gnupg.py

@@ -116,7 +116,11 @@ class PGP(gnupg.GPG, metaclass=Singleton):
 
         for key in result:
             # Take first not empty uid
-            keys[key['fingerprint']] = next(uid for uid in key['uids'] if uid)
+            try:
+                keys[key['fingerprint']] = next(uid for uid in key['uids'] if uid)
+            except StopIteration:
+                # No key non-empty uids present
+                keys[key['fingerprint']] = ''
         return keys
 
     @staticmethod