Minimal reproducer:

--8<---------------cut here---------------start------------->8---
(use-modules (gnu services configuration)
             (gnu packages mail))

(define-configuration/no-serialization home-goimapnotify-configuration
  (package
    (package go-gitlab.com-shackra-goimapnotify)
    "The @code{goimapnotify} package to use."))

(generate-documentation
 `((home-goimapnotify-configuration
    ,home-goimapnotify-configuration-fields))
 'home-goimapnotify-configuration)
--8<---------------cut here---------------end--------------->8---

Error:

--8<---------------cut here---------------start------------->8---
(generate-documentation
 `((home-goimapnotify-configuration
    ,home-goimapnotify-configuration-fields))
 'home-goimapnotify-configuration)

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
In procedure symbol->string: Wrong type argument in position 1 (expecting symbol): #f


[Debugging level: 18]
--8<---------------cut here---------------end--------------->8---

I suspect that problematic code is here:
https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/services/configuration.scm?h=6505f727e1824391b888dd0c2c60cf64ec66955a#n308

-- 
Best regards,
Andrew Tropin