Can't attach solidity-lsp for .sol files in neovim - solidity

Question

Firtsble solidity-ls installed by mason via neovim command
:LspInstall solidity-ls
wasn't executable from terminal, altough it was shown as an executable one when typing :LspInfo in .sol file. After I installed it manually via npm
npm i solidity-ls -g
This is configuration for solidity-ls
require'lspconfig'.solidity.setup({
on_attach = on_attach,
})
With this empty configuration however root directory is not found, also solidity-ls is not attached to the file which I guess is just a consequence.
After adding root_dir manually in a following way and checking the file via luafile %
require'lspconfig'.solidity.setup({
on_attach = on_attach,
root_dir = function(fname)
return vim.fn.getcwd()
end,
})
I get this error
LSP[solidity]: Error SERVER_REQUEST_HANDLER_ERROR: "/usr/share/nvim/runtime/lua/vim/lsp/handlers.lua:86: bad argument #1 to 'ipairs' (table expected, got nil)"
Although :LspInfo shows root_dir is set up solidity-ls still is not attached
LspInfo from .sol file after
Any suggestion how to solve this?
Ubuntu 20.04.3 LTS
NVIM v0.7.2
I am new in vim, neovim and lua programming so apologizes in advance in case the question is too silly. Thanks.