### Please describe the problem.

As of a14f6ce75 (fix repo description setting bugs, 2019-05-23), `git annex init` without a description sets the description to a blank string.  AFAICT from the description of that change and from the corresponding [bug report][0], that isn't an intentional change.

[0]: https://git-annex.branchable.com/bugs/git-annex-init_with_no_args_overwrites_existing_repo_description/
### What steps will reproduce the problem?

```
cd $(mktemp -dt gx-XXXXXXX)
git init
git annex init
git annex info --json | jq
```

On the parent of a14f6ce75, this shows

```
Initialized empty Git repository in /tmp/gx-BLmU7TJ/.git/
init  ok
(recording state in git...)
{
  "local annex size": "0 bytes",
  "size of annexed files in working tree": "0 bytes",
  "command": "info",
  "untrusted repositories": [],
  "success": true,
  "semitrusted repositories": [
    {
      "here": false,
      "uuid": "00000000-0000-0000-0000-000000000001",
      "description": "web"
    },
    {
      "here": false,
      "uuid": "00000000-0000-0000-0000-000000000002",
      "description": "bittorrent"
    },
    {
      "here": true,
      "uuid": "d1ef2ae8-9604-4c33-8c3c-181f81c4348f",
      "description": "kyle@hylob:/tmp/gx-BLmU7TJ"
    }
  ],
  "bloom filter size": "32 mebibytes (0% full)",
  "repository mode": "indirect",
  "backend usage": {},
  "transfers in progress": [],
  "local annex keys": 0,
  "available local disk space": "301.33 gigabytes (+1 megabyte reserved)",
  "annexed files in working tree": 0,
  "file": null,
  "trusted repositories": []
}
```

On a14f6ce75, this shows

```
Initialized empty Git repository in /tmp/gx-pK345zF/.git/
init  ok
{
  "local annex size": "0 bytes",
  "size of annexed files in working tree": "0 bytes",
  "command": "info",
  "untrusted repositories": [],
  "success": true,
  "semitrusted repositories": [
    {
      "here": false,
      "uuid": "00000000-0000-0000-0000-000000000001",
      "description": "web"
    },
    {
      "here": false,
      "uuid": "00000000-0000-0000-0000-000000000002",
      "description": "bittorrent"
    },
    {
      "here": true,
      "uuid": "00b8da69-41a5-4de8-9a6a-9ed991289f81",
      "description": ""
    }
  ],
  "bloom filter size": "32 mebibytes (0% full)",
  "repository mode": "indirect",
  "backend usage": {},
  "transfers in progress": [],
  "local annex keys": 0,
  "available local disk space": "301.22 gigabytes (+1 megabyte reserved)",
  "annexed files in working tree": 0,
  "file": null,
  "trusted repositories": []
}
```

Note that the description for here is a blank string.

> [[fixed|done]] --[[Joey]]
[[!meta author=kyle]]
[[!tag projects/repronim]]
