tags-query-replace leads to calling expand-file-name on nil

[Yevgeniy Makarov]

Hello,

I am getting an error while doing tags-query-replace. Below is the
trace with debug-on-error on:

  expand-file-name(nil)
  tags-expand-table-name(nil)
  visit-tags-table-buffer(t)
  next-file(t t)
  tags-loop-continue(t)
  tags-query-replace("nondep_induct" "cases" nil)

Maybe I don't understand how to tell Emacs where tags are stored. The
Emacs manual says I can define the variable tags-table-list. But what
if I have separate projects in different directories? If I put the
tables for different projects in the same list, does it mean that tag
search and replace will be done on all files listed in all tables?

So I added comments to every file in the project that set the file
variable as follows:

(*
 Local Variables:
 tags-file-name: "~/coq/trunk/theories/Numbers/TAGS"
 End:
*)

Is this OK?

Thank you,
Yevgeniy