function need attr table if is nil add empty table

[KamiALK]

While working with the jdtls configuration in Neovim, I noticed that in certain cases, the opts.jdtls field might not be defined, leading to an error when trying to merge configurations using vim.tbl_deep_extend. To avoid this issue, I added a check that passes an empty table {} if opts.jdtls is nil.
I modified the attach_jdtls function so that when constructing the language server configuration, opts.jdtls or {} is passed to the vim.tbl_deep_extend call. This ensures that a valid table is always passed, preventing unexpected errors and improving the robustness of the code.