Endpoints resource [#78016138]

what if `cert_path` is provided without `key_path` (so `key_path` is `nil`)? user will see error from line 84 and then `::File.read(key_path)` (`::File.read(nil)`) will raise an exception, right?

maybe better would be something like this:
```ruby
if cert_path && key_path
  ...
else
  say_error "provide ..."
end
```