Cannot deprecate module in private registry - "'url' must be a string"

When I run this

npm deprecate x "x is gone bad" --registry=https://example.com/npm/

I get that

npm ERR! Darwin 14.5.0
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "deprecate" "x" "x is gone bad" "--registry=https://example.com/npm/"
npm ERR! node v4.1.0
npm ERR! npm  v2.14.3

npm ERR! Parameter 'url' must be a string, not undefined
npm ERR! 
npm ERR! If you need help, you may report this error at:
npm ERR!     <https://github.com/npm/npm/issues>

npm ERR! Please include the following file with any support request:
npm ERR!     /pth/x/npm-debug.log

This is true also if I do --registry https://example.com/npm/ (space instead of equal) or leave out the --registry parameter altogether (it's in my .npmrc).

I have been able to publish and update the module to that registry without any problems; only deprecate seems not to work.

Using OS X. Here's the npm-debug.log

0 info it worked if it ends with ok
1 verbose cli [ '/usr/local/bin/node',
1 verbose cli   '/usr/local/bin/npm',
1 verbose cli   'deprecate',
1 verbose cli   'x',
1 verbose cli   'x gone bad',
1 verbose cli   '--registry=http://example.com/npm/' ]
2 info using npm@2.14.3
3 info using node@v4.1.0
4 silly mapToRegistry name x
5 silly mapToRegistry using default registry
6 silly mapToRegistry registry http://example.com/npm/
7 silly mapToRegistry uri http://example.com/npm/x
8 verbose get GET as part of write; not caching result
9 verbose request uri http://example.com/npm/x?write=true
10 verbose request always-auth set; sending authorization
11 info attempt registry request try #1 at 11:33:01 AM
12 verbose request id 06b2d6060e33ed7c
13 http request GET http://example.com/npm/x?write=true
14 http 200 http://example.com/npm/x?write=true
15 silly get cb [ 200,
15 silly get   { date: 'Fri, 09 Oct 2015 09:32:56 GMT',
15 silly get     server: 'Nexus/2.11.1-01',
15 silly get     'x-frame-options': 'SAMEORIGIN',
15 silly get     'x-content-type-options': 'nosniff',
15 silly get     'accept-ranges': 'bytes',
15 silly get     'content-type': 'application/json',
15 silly get     'last-modified': 'Fri, 09 Oct 2015 09:32:56 GMT',
15 silly get     'content-length': '63950',
15 silly get     'set-cookie': [ 'rememberMe=deleteMe; Path=/; Max-Age=0; Expires=Thu, 08-Oct-2015 09:32:56 GMT' ],
15 silly get     'keep-alive': 'timeout=5, max=100',
15 silly get     connection: 'Keep-Alive' } ]
16 verbose get saving x to /path/.npm/xxx/content/groups/npm-default/x_3Fwrite_3Dtrue/.cache.json
17 verbose stack TypeError: Parameter 'url' must be a string, not undefined
17 verbose stack     at Url.parse (url.js:90:11)
17 verbose stack     at urlParse (url.js:84:5)
17 verbose stack     at Url.resolve (url.js:426:29)
17 verbose stack     at Object.urlResolve [as resolve] (url.js:422:40)
17 verbose stack     at CachingRegistryClient.<anonymous> (/usr/local/lib/node_modules/npm/node_modules/npm-registry-client/lib/deprecate.js:41:22)
17 verbose stack     at saved (/usr/local/lib/node_modules/npm/lib/cache/caching-client.js:173:7)
17 verbose stack     at /usr/local/lib/node_modules/npm/node_modules/graceful-fs/polyfills.js:210:7
17 verbose stack     at FSReqWrap.oncomplete (fs.js:82:15)
18 verbose cwd /path/work/pv-frontend-build-tools/x
19 error Darwin 14.5.0
20 error argv "/usr/local/bin/node" "/usr/local/bin/npm" "deprecate" "x" "x gone bad" "--registry=http://example.com/npm/"
21 error node v4.1.0
22 error npm  v2.14.3
23 error Parameter 'url' must be a string, not undefined
24 error If you need help, you may report this error at:
24 error     <https://github.com/npm/npm/issues>
25 verbose exit [ 1, true ]

npm / npm-registry-client

Cannot deprecate module in private registry - "'url' must be a string" #120