From 9739de9244cf81682485ae4e29c8f11060d3aee5 Mon Sep 17 00:00:00 2001
From: esteele <eric@esteele.net>
Date: Fri, 18 Sep 2015 14:54:22 +0200
Subject: [PATCH] Only try to convert strings.

---
 plone/app/upgrade/v50/betas.py | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/plone/app/upgrade/v50/betas.py b/plone/app/upgrade/v50/betas.py
index cfd2bc54..e08bcbe0 100644
--- a/plone/app/upgrade/v50/betas.py
+++ b/plone/app/upgrade/v50/betas.py
@@ -497,17 +497,18 @@ def to50rc3(context):
             portal._delProperty(p)
 
     properties_to_migrate = ['external_links_open_new_window',
-							 'mark_special_links',
+                             'mark_special_links',
                              'calendar_starting_year',
                              'calendar_future_years_available',
-							 'redirect_links']
+                             'redirect_links']
     for p in properties_to_migrate:
         if site_properties.hasProperty(p):
             value = site_properties.getProperty(p)
-            if value.lower() == 'true':
-                value = True
-            elif value.lower() == 'false':
-                value = False
+            if isinstance(value, basestring):
+                if value.lower() == 'true':
+                    value = True
+                elif value.lower() == 'false':
+                    value = False
             try:
                 registry['plone.%s' % p] = value
                 site_properties._delProperty(p)