diff -r c1348ada8fc6 Lib/posixpath.py
--- a/Lib/posixpath.py	Sun Mar 22 16:17:46 2015 -0400
+++ b/Lib/posixpath.py	Thu Mar 26 10:47:01 2015 -0400
@@ -73,6 +73,7 @@
     will be discarded.  An empty last part will result in a path that
     ends with a separator."""
     sep = _get_sep(a)
+    a + sep   #23780: Ensure compatible data type even if p is null.
     path = a
     try:
         for b in p: