The patch to org-eldoc applied in b2b587387 still throws an error:

eldoc error: (void-function nil)

I was unable to step through this because (I think) eldoc causes 
the debugger to close as soon as input is received. The error 
occurs when `eldoc--invoke-strategy` attempts to funcall 
eldoc-documentation-default.

The attached patch works for me, but I do not know if it is the 
correct solution.

Emacs  : GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, X 
toolkit, cairo version 1.17.3, Xaw3d scroll bars)
 of 2020-08-12
Package: Org mode version 9.3.7 (release_9.3.7-708-g5417e3 @ 
/home/n/.emacs.d/straight/build/org/)