Integer labels cannot be deleted through REST API

Summary

It is not possible to delete integer labels through the REST API.

Steps to Reproduce

1. Add an all-integer label to a page (2016 for example)
2. Run the following curl command to delete it:
   {code}
   curl -v -S -u <username>:<password> -X DELETE http://<domain>/rest/api/content/66755/label?name=2016
   {code}

Expected Results

Label is deleted and the following output is shown in the console:

{code}

• Trying 192.168.10.10...
• Connected to quicksilver (127.0.0.1) port 80 (#0)
• Server auth using Basic with user 'admin'
  > DELETE /confluence/rest/api/content/66755/label?name=test_lable HTTP/1.1
  > Host: quicksilver
  > Authorization: Basic YWRtaW46YWRtaW4=
  > User-Agent: curl/7.43.0
  > Accept: /
  >
  < HTTP/1.1 204 No Content
  < Date: Wed, 08 Nov 2017 19:36:02 GMT
  < Server: Apache-Coyote/1.1
  < X-ASEN: SEN-L5422754
  < X-Seraph-LoginReason: OK
  < X-AUSERNAME: admin
  < Cache-Control: no-cache, must-revalidate
  < Expires: Thu, 01 Jan 1970 00:00:00 GMT
  < X-Content-Type-Options: nosniff
  < Content-Type: application/json
  < Set-Cookie: JSESSIONID=C6ABA446ACA2497051852585C3B019AB; Path=/confluence; HttpOnly
  <
• Connection #0 to host quicksilver left intact
  {code}

Actual Results

Label is not deleted and a 500 error is returned with messageKey=label.not.found:

{code}

• Trying 192.168.10.10...
• Connected to quicksilver (127.0.0.1) port 80 (#0)
• Server auth using Basic with user 'admin'
  > DELETE /confluence/rest/api/content/66755/label?name=2016 HTTP/1.1
  > Host: quicksilver
  > Authorization: Basic YWRtaW46YWRtaW4=
  > User-Agent: curl/7.43.0
  > Accept: /
  >
  < HTTP/1.1 500 Internal Server Error
  < Date: Wed, 08 Nov 2017 19:36:26 GMT
  < Server: Apache-Coyote/1.1
  < X-ASEN: SEN-L5422754
  < X-Seraph-LoginReason: OK
  < X-AUSERNAME: admin
  < Cache-Control: no-cache, must-revalidate
  < Expires: Thu, 01 Jan 1970 00:00:00 GMT
  < X-Content-Type-Options: nosniff
  < Content-Type: application/json
  < Set-Cookie: JSESSIONID=09567DCB359114A39EDB4558CED13A2D; Path=/confluence; HttpOnly
  < Connection: close
  < Transfer-Encoding: chunked
  <
• Closing connection 0
  {"statusCode":500,"message":"com.atlassian.confluence.core.service.NotValidException: [ValidationError [messageKey=label.not.found, args=[]]]"}
  {code}

Notes

Labels that contain letters can be successfully deleted. It is also not possible to delete them through the label ID.

Workaround

No known workaround at the moment.