Author: Mikael Magnusson <mikma@users.sourceforge.net>
Forwarded: https://github.com/dap/XML-Stream/issues/14
Description: Fix an 'uninitialized value' warning

--- a/lib/XML/Stream.pm
+++ b/lib/XML/Stream.pm
@@ -2164,7 +2164,12 @@
         $response = $self->{SIDS}->{$sid}->{sasl}->{client}->client_step($challenge);
     }
 
-    my $response64 = MIME::Base64::encode_base64($response,"");
+    my $response64 = "";
+    if (defined $response)
+    {
+        $response64 = MIME::Base64::encode_base64($response,"");
+    }
+
     $self->SASLResponse($sid,$response64);
 }