This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
According to 13.8 [temp.res] paragraph 8,
No diagnostic shall be issued for a template for which a valid specialization can be generated.
One sentence later, it says,
If every valid specialization of a variadic template requires an empty template parameter pack, the template is ill-formed, no diagnostic required.
This appears to be a contradiction: in the latter case, there is postulated to exist a “valid” specialization (with an empty pack expansion), for which a diagnostic might or might not be issued. The first quoted sentence, however, forbids issuing a diagnostic for a template that has at least one valid specialization.
Rationale (February, 2017):
The text in question was revised editorially and the issue is now moot.