patch 7.4.1654
Problem: Crash when using expand('%:S') in a buffer without a name.
Solution: Don't set a NUL. (James McCoy, closes #714)
diff --git a/src/testdir/test_fnamemodify.vim b/src/testdir/test_fnamemodify.vim
index 902be40..2267e18 100644
--- a/src/testdir/test_fnamemodify.vim
+++ b/src/testdir/test_fnamemodify.vim
@@ -41,3 +41,9 @@
call assert_equal("'abc\\\ndef'", fnamemodify("abc\ndef", ':S'))
set shell&
endfunc
+
+func Test_expand()
+ new
+ call assert_equal("", expand('%:S'))
+ quit
+endfunc