omnifunc documentation popup not throw error

omnifunc documentation popup not throw error
When using Omni completion with other sources of completion items
that do not have 'user_data' dictionary, documentation popup should
not throw error.

I am using my own completion plugin with g:LspOmniFunc and I need
LSP to grab lazy-doc from lsp server. But it should not throw
error when user_data does not contain dictionary.

M  autoload/lsp/completion.vim