Another texinfo error

[Daniel J S. <dan...@ie...>]

Introduced within the passed few days, I think:

Loading /usr/share/emacs/site-lisp/site-start.d/rpm-spec-mode-init.el (source)...
Inserting help for terminals ...
Analyzing doc file ...
Converting to texinfo ...
Menus, nodes, xrefs ...
Wrong type argument: stringp, nil
make[1]: *** [gnuplot.texi] Error 255
make[1]: Leaving directory `/usr/local/src/gnuplot-key/gnuplot/docs'
make: *** [install-recursive] Error 1