patch 7.4.1081
Problem:    No test for what previously caused a crash.
Solution:   Add test for unletting errmsg.
diff --git a/src/testdir/test_unlet.vim b/src/testdir/test_unlet.vim
index f670599..13ec66b 100644
--- a/src/testdir/test_unlet.vim
+++ b/src/testdir/test_unlet.vim
@@ -7,6 +7,12 @@
   catch
     call assert_true(v:exception =~ ':E795:')
   endtry
+  try
+    " this caused a crash
+    unlet errmsg
+  catch
+    call assert_true(v:exception =~ ':E795:')
+  endtry
 endfunc
 
 func Test_existing()