Exception on `guix import`

[Joseph LaFreniere]

Running `guix import pypi black-macchiato` prints the following 
output (also attached):

```
Backtrace:
In ice-9/boot-9.scm:
 1736:10 18 (with-exception-handler _ _ #:unwind? _ 
 #:unwind-for-type _)
In unknown file:
         17 (apply-smob/0 #<thunk 7ff90938b2c0>)
In ice-9/boot-9.scm:
   718:2 16 (call-with-prompt _ _ #<procedure 
   default-prompt-handler (k proc)>)
In ice-9/eval.scm:
   619:8 15 (_ #(#(#<directory (guile-user) 7ff908fb0f00>)))
In guix/ui.scm:
 2115:12 14 (run-guix-command _ . _)
In guix/scripts/import.scm:
  120:11 13 (guix-import . _)
In guix/scripts/import/pypi.scm:
   99:23 12 (guix-import-pypi . _)
In guix/memoization.scm:
    98:0 11 (mproc "black-macchiato")
In unknown file:
         10 (_ #<procedure 7ff906dbf580 at 
         guix/memoization.scm:179:32 ()> #<procedure list _> 
         ("black-macchiato"))
In guix/import/pypi.scm:
  477:21  9 (_ _)
   121:9  8 (pypi-fetch "black-macchiato")
In guix/import/json.scm:
    45:2  7 (json-fetch _ #:headers _)
In ice-9/boot-9.scm:
 1736:10  6 (with-exception-handler _ _ #:unwind? _ 
 #:unwind-for-type _)
In guix/import/json.scm:
   50:19  5 (_)
In guix/http-client.scm:
   87:25  4 (http-fetch _ #:port _ #:text? _ #:buffered? _ 
   #:verify-certificate? _ #:headers _)
In guix/build/download.scm:
   436:4  3 (open-connection-for-uri _ #:timeout _ 
   #:verify-certificate? _)
  437:14  2 (thunk)
  361:16  1 (open-socket-for-uri _ #:timeout _)
In ice-9/boot-9.scm:
 1669:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1669:16: In procedure raise-exception:
In procedure struct-vtable: Wrong type argument in position 1 
(expecting struct): #f
```

I am getting this exception with guix 1.1.0-28.d27dbeb on Guix 
System.  The same exception is also occurring when running `guix 
import elpa -a melpa python-black`.

--
Joseph LaFreniere

output.txt
Description: Text document