why %s/b//gn doesn't work?

If I want to replace the `b` letter in the text with `null` and I also want to get the match number.

so I use the command `%s/b//gn` , but I just get the count number but the `b` letter hasn't been replaced.

If I use %s/b/a/gn it worked.

How can I fix this problem?

I want to delete the `b` letter and the know the count number mean time . What should I do?

--
--
You received this message from the "vim_use" maillist.
Do not top-post! Type your reply below the text you are replying to.
For more information, visit http://www.vim.org/maillist.php

---
You received this message because you are subscribed to the Google Groups "vim_use" group.
To unsubscribe from this group and stop receiving emails from it, send an email to vim_use+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.