Why adapter.port is needed for function type adapter?

[LumenYoung]

Hi, I'm encountering issue with using a custom adapter as follow:

  adapters = {
    generic_remote = function(callback, config)
      local port = (config.connect or config).port
      local host = (config.connect or config).host or '127.0.0.1'
      callback({
        type = 'server',
        host = host,
        port = port,
      })
    end
  },

But when I run it, I get the following error trace:

...l/share/lunarvim/site/pack/lazy/opt/nvim-dap/lua/dap.lua:1015: Adapter used with attach must have a port property
stack traceback:
	[C]: in function 'assert'
	...l/share/lunarvim/site/pack/lazy/opt/nvim-dap/lua/dap.lua:1015: in function 'attach'
	...l/share/lunarvim/site/pack/lazy/opt/nvim-dap/lua/dap.lua:376: in function 'run_adapter'
	...l/share/lunarvim/site/pack/lazy/opt/nvim-dap/lua/dap.lua:408: in function 'maybe_enrich_config_and_run'
	...l/share/lunarvim/site/pack/lazy/opt/nvim-dap/lua/dap.lua:509: in function 'callback'
	./.nvim-dap.lua:7: in function 'adapter'
	...l/share/lunarvim/site/pack/lazy/opt/nvim-dap/lua/dap.lua:507: in function <...l/share/lunarvim/site/pack/lazy/opt/nvim-dap/lua/dap.lua:488>
	[C]: in function 'xpcall'
	...e/lunarvim/site/pack/lazy/opt/nvim-dap/lua/dap/async.lua:12: in function <...e/lunarvim/site/pack/lazy/opt/nvim-dap/lua/dap/async.lua:11>

Which lead back to the source code here. Since the example I'm after and doc all didn't mention such requirement of port, nor am I very familiar with lua. Can I get advice on how I should resolve this error? Thanks