diff --git a/poky/meta/lib/oe/utils.py b/poky/meta/lib/oe/utils.py
index 468c76f..9a2187e 100644
--- a/poky/meta/lib/oe/utils.py
+++ b/poky/meta/lib/oe/utils.py
@@ -193,7 +193,7 @@
 
         return int(v)
 
-    return None
+    return ''
 
 def parallel_make_argument(d, fmt, limit=None, makeinst=False):
     """