Hide non translated keys in custom locales

[fernion]

Hello all,

I have a project where we have custom language files for some customers. Something like:

📁locales/
  📁en/
    🗎 messages.json
  📁en-customer1/
    🗎 messages.json

en-customer1 is configured as having en as fallback.

Currently with the extract command we get a lot of empty translations in the en-customer1/messages.json file.
Is there a way to configure lingui so that it does not create these keys on some locales (for example, a pre-set list or the ones that have fallback)?
The deletion of unused keys is still required though.

Basically instead of having:

//en/message.json
{
  "Some value": "Some value",
  "Another value": "Another value"
}
//en-customer1/message.json
{
  "Some value": "Some different value",
  "Another value": ""
}

we were trying to achieve:

//en/message.json
{
  "Some value": "Some value",
  "Another value": "Another value"
}
//en-customer1/message.json
{
  "Some value": "Some different value"
}

Thank you.