Config `api_key_cmd` did not return a value when executed

I love this plugin but I can't make it work.

I use Plug to install it:

```
Plug 'jackMort/ChatGPT.nvim'
Plug 'MunifTanjim/nui.nvim'
Plug 'nvim-lua/plenary.nvim'
Plug 'nvim-telescope/telescope.nvim'
```

I have a `secret.txt.gpg` in my home directory that was encrypted with the following command:

`gpg --encrypt --recipient [my email] secret.txt`

The contents of the `secret.txt` are `$OPENAI_API_KEY=xxxxxxxxxxxxxxxx`

And I try to get the `OPENAI_API_KEY` like so:

```
local home = vim.fn.expand("$HOME")
require("chatgpt").setup({
api_key_cmd = "gpg --decrypt " .. home .. "/secret.txt.gpg"
})
```

The error I'm getting is **Config `api_key_cmd` did not return a value when executed**

What am I doing wrong here ?

Thanks!

Start at the api_key_cmd option passed to require('chatgpt').setup and inspect how its command output is read. Reproduce the shown gpg command and verify that it returns a non-empty API-key value, then confirm setup completes without the reported error.

Written by the indexing model from the issue text.