`kcr list` always lists a `null` client among the rest

[kkga]

I'm not sure if this is expected, so feel free to close if it is.

Basically, the list of sessions always contains a client: null object per each session.

kcr is nightly-9-g9012fba on macOS, but the same happens on Linux.

[
  {
    "session": "5045",
    "client": null,
    "buffer_name": null,
    "working_directory": "/Users/kkga/projects/nine-nines"
  },
  {
    "session": "5045",
    "client": "client0",
    "buffer_name": "index.html",
    "working_directory": "/Users/kkga/projects/nine-nines"
  },
  {
    "session": "5045",
    "client": "client1",
    "buffer_name": "index.html",
    "working_directory": "/Users/kkga/projects/nine-nines"
  },
  {
    "session": "4715",
    "client": null,
    "buffer_name": null,
    "working_directory": "/Users/kkga/notes/webflow"
  },
  {
    "session": "4715",
    "client": "client0",
    "buffer_name": "section-and-cells.md",
    "working_directory": "/Users/kkga/notes/webflow"
  }
]

[alexherbo2]

It is used to see and connect to headless sessions.