presets v3: cannot --list-presets if generator omitted

Version 3 of CMake Presets allows omitting the generator from CMakePresets.json. However, cmake --list-presets emits nothing when generator is omitted, despite the presets otherwise working. This is with CMake 3.21.0-rc2.

{
  "version": 3,

"configurePresets": [
{
  "name": "default",
  "generator": "Ninja"
}
]
}

Available configure presets:

  "default"

the above works with cmake --list-presets. The following emits nothing for the same command:

{
  "version": 3,

"configurePresets": [
{
  "name": "default"
}
]
}

For my real CMakePresets.json, I have more parameters but the same symptoms persist.