How can I check if NoneLS uses formatting for the current buffer?

[acid-bong]

I'm trying to set up format-on-save handler, which currently looks like this:

local format_autocmd = function(bufnr, filter)
  vim.api.nvim_create_autocmd("BufWritePre", {
    buffer = bufnr,
    group = "LspFormat",
    callback = function()
      vim.lsp.buf.format {
        bufnr = bufnr,
        filter = if filter then -- prolly not valid lua, not the point
          function(c) return c.name == "null-ls" end
        else
          nil
        end
      }
    end,
  })
end

vim.api.nvim_create_augroup("LspFormat", {})
vim.api.nvim_create_autocmd("LspAttach", {
  callback = function(args)
    local bufnr = args.buf
    -- format on save
    format_autocmd(bufnr, false)
    local clients = vim.lsp.get_clients {
      bufnr = bufnr,
    }
    for _, client in ipairs(clients) do
      if client.name == "null-ls" then
        vim.api.nvim_clear_autocmds {
          buffer = bufnr,
          group = "LspFormat",
        }
        format_autocmd(bufnr, true)
        break
      end
    end
  end,
})

This has one issue tho: if I use NoneLS in a specific ft not for formatting (like extra code actions, unsupported by the main LS), this'll set the formatting to NoneLS anyway, which is not always desired.

How can I detect if NoneLS uses a formatter locally?