bug#69209: Extended packaging example from the Guix cookbook produces an error

[Balthazar Potet]

Hello,

I tried to install the package defined in this section of the Guix
cookbook : https://guix.gnu.org/cookbook/en/guix-cookbook.html#Extended-example

Running `guix package -f example.scm` gives the following error:

Backtrace:
In guix/store.scm:
  2180:25 19 (run-with-store #<store-connection 256.99 7fea884c5dc0> …)
In guix/gexp.scm:
   914:13 18 (_ _)
In guix/store.scm:
   2008:8 17 (_ _)
In guix/gexp.scm:
   299:22 16 (_ _)
In guix/store.scm:
   2008:8 15 (_ _)
In guix/packages.scm:
  1977:11 14 (_ _)
In guix/gexp.scm:
   1201:2 13 (_ #<store-connection 256.99 7fea863822d0>)
   1068:2 12 (_ _)
    909:4 11 (_ _)
In guix/store.scm:
  2065:12 10 (_ #<store-connection 256.99 7fea863822d0>)
  1382:11  9 (map/accumulate-builds #<store-connection 256.99 7fea8…> …)
   1300:8  8 (call-with-build-handler #<procedure 7fea85e07ea0 at g…> …)
  2180:25  7 (run-with-store #<store-connection 256.99 7fea863822d0> …)
In guix/gexp.scm:
   914:13  6 (_ _)
In guix/store.scm:
  2008:13  5 (_ #<store-connection 256.99 7fea863822d0>)
In guix/gexp.scm:
   299:51  4 (_)
In guix/packages.scm:
   2081:2  3 Exception thrown while printing backtrace:
error: search-patches: unbound variable

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
error: search-patches: unbound variable