[Bug] Error executing vim.schedule

[YuCao16]

This bug may not be a problem with lsp_signature.nvim, but I still hope you can take a look at it.

Reproduce:

1. Install pandas and pandas-stubs library (python and pip)
2. create a python script with following code (put cursor inside quote)

   import pandas as pd
   pd.read_csv("")

   Then following error appear:

   Error executing vim.schedule lua callback: ...lar/neovim/0.8.1/share/nvim/runtime/lua/vim/lsp/util.lua:1577: String cannot contain newlines                                                                          
   stack traceback:                                                                                                                                                                                                     
       [C]: in function 'nvim_buf_set_lines'                                                                                                                                                                        
       ...lar/neovim/0.8.1/share/nvim/runtime/lua/vim/lsp/util.lua:1577: in function 'open_floating_preview'                                                                                                        
       ...packer/opt/lsp_signature.nvim/lua/lsp_signature/init.lua:520: in function 'handler'                                                                                                                       
       ...w/Cellar/neovim/0.8.1/share/nvim/runtime/lua/vim/lsp.lua:1383: in function ''                                                                                                                             
       vim/_editor.lua: in function <vim/_editor.lua:0>   

If I uninstall pandas-stubs, then the error will not arise.

[ray-x]

Could you check if it still occurs in the latest version?

[kasfil]

i had similar issue while using pytest updated to the master branch. i can confirm this issue already fixed