diff --git a/fsl/props/properties.py b/fsl/props/properties.py
index dfa5b5f9bd9c2ef547991ef40a9a7c4c7cb27e7e..2ce875b93271d2c30c7d99a0c6683d7986860182 100644
--- a/fsl/props/properties.py
+++ b/fsl/props/properties.py
@@ -116,7 +116,6 @@
 
 import logging
 
-from collections import OrderedDict
 
 log = logging.getLogger(__name__)
 
diff --git a/fsl/props/properties_types.py b/fsl/props/properties_types.py
index 328ef10d135b66736f1db1e529f8b5edce15ea35..7423ae8cac0dc28c6bfa383cc538a38092dfc7aa 100644
--- a/fsl/props/properties_types.py
+++ b/fsl/props/properties_types.py
@@ -139,8 +139,10 @@ class String(props.PropertyBase):
 
 
     def cast(self, value):
+
+        if value is None: value = ''
+        else:             value = str(value)
         
-        value = str(value)
         if value == '': value = None
         return value