only cleanup string if not None

Author: timvaillancourt

mongodb_consistent_backup/Common/DB.py

@@ -27,12 +27,15 @@ def __init__(self, uri, config, do_replset=False, read_pref='primaryPreferred',
         self.ssl_ca_file          = self.config.ssl.ca_file
         self.ssl_crl_file         = self.config.ssl.crl_file
         self.ssl_client_cert_file = self.config.ssl.client_cert_file
-        self.read_pref_tags       = self.config.replication.read_pref_tags.replace(" ", "")
+        self.read_pref_tags       = self.config.replication.read_pref_tags
 
         self.replset    = None
         self._conn      = None
         self._is_master = None
 
+        if self.read_pref_tags:
+            self.read_pref_tags = self.read_pref_tags.replace(" ", "")
+
         self.connect()
         self.auth_if_required()