diff --git a/python/fileformat.py b/python/fileformat.py
index df588a4..fd1b71a 100644
--- a/python/fileformat.py
+++ b/python/fileformat.py
@@ -54,6 +54,9 @@ def read_action(lines):
 
 def write_field_value_str(val):
     lines = ''
+    if not val:
+        val = ''
+    val = unicode(val)
     value_lines = val.split('\n')
     for l in value_lines:
         lines += ' ' + l + '\n'
@@ -63,13 +66,13 @@ def write_field_value_dict(val):
     lines = '\n'
     for (key,values) in val.items():
         for single_value in values:
-            lines += ' ' + key + ' ' + single_value + '\n'
+            lines += ' ' + key + ' ' + unicode(single_value) + '\n'
     return lines
 
 def write_field_value_list(val):
     lines = ''
     for single_value in val:
-        lines += ' ' + single_value
+        lines += ' ' + unicode(single_value)
     return lines
 
 def write_action(d):