From an email to cxxeditor@:

27.6.3.4.5 [streambuf.virt.put] p5 says:

at pbase() are the associated output stream. In case r is zero (all
characters of the pending
sequence have been consumed) then either pbase() is set to NULL, or
pbase() and pptr() are
both set to the same NULL non-value.

I'm assuming that should be non-NULL value, because I don't think we
want to set them to a non-value!