Hello all,

For few days now, I have been seeing the "wrong-type-argument avl-tree-" error when I try to kill a buffer where org-persist has run.

I am seeing this with the latest build of emacs-28 branch plus org main branch as of today.

Here's the backtrace:

Debugger entered--Lisp error: (wrong-type-argument avl-tree- nil)
  avl-tree-mapc(#<subr F616e6f6e796d6f75732d6c616d626461_anonymous_lambda_80> nil)
  org-element--cache-persist-before-write(org-element--cache #<buffer NEWS>)
  run-hook-with-args-until-success(org-element--cache-persist-before-write org-element--cache #<buffer NEWS>)
  #f(compiled-function (v) #<bytecode -0x12583f23e316161a>)(org-element--cache)
  #f(compiled-function (elt) #<bytecode -0x5162c688172baba>)(org-element--cache)
  mapc(#f(compiled-function (elt) #<bytecode -0x5162c688172baba>) (org-element--headline-cache org-element--cache))
  seq-do(#f(compiled-function (elt) #<bytecode -0x5162c688172baba>) (org-element--headline-cache org-element--cache))
  seq-find(#f(compiled-function (v) #<bytecode -0x12583f23e316161a>) (org-element--headline-cache org-element--cache))
  org-persist-write((org-element--headline-cache org-element--cache) #<buffer NEWS>)
  org-persist-write-all(#<buffer NEWS>)
  org-persist-write-all-buffer()
  kill-buffer("NEWS")