error tangling: how to debug please?

["Fraga, Eric" <e.fraga@ucl.ac.uk>]

Hello all,

I have a rather large & complex file which has many src blocks, all of
which tangle to a single file, defined by a header-args property.

When I try to tangle, I get the following (not very informative
unfortunately) backtrace:

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  org-src-coderef-regexp(nil)
  org-babel-tangle-single-block(1)
  org-babel-tangle-collect-blocks(nil nil)
  org-babel-tangle(nil)
  funcall-interactively(org-babel-tangle nil)
  command-execute(org-babel-tangle)

This is with both Emacs and org up to date with respect to the
repositories as of a minute or two ago.

I haven't tried emacs -Q or similar as there are too many things to set
up for this complex file.  I am just looking for any hints or
suggestions that could help me debug this.

Thank you,
eric

-- 
: Eric S Fraga, with org release_9.6.7-661-g34ee6f in Emacs 30.0.50