def write_boilerplate(project_name) do
    file_name = project_name <> ".ex"
    file_path = Path.join([project_name, file_name])
    boilerplate = "defmodule #{project_name} do\nend"
    File.write(file_path, boilerplate, mode: :append)
  end

the LSP i use is elixir_ls
what happens is the code runs smoothly but while in neovim i get this strange warning:

The function call will not succeed. File.write(_file_path :: binary(), _boilerplate :: <<_::8, _::size(1)>>, [{:mode, :append}]) breaks the contract (Path.t(), iodata(), [mode()]) :: :ok | {:error, posix()} 

why is this happening? can’t find an answer in the docs.