How to use key with a dot at the end?

Eg:

"This is a sentence.": "This is the result sentence."

I got an error that the YAML file becomes an empty path if I put a dot behind the key, how can I solve this?

EDIT: I got this error:

java.lang.IllegalArgumentException: Cannot set to an empty path

when using this:

FileConfiguration langPack_EN = YamlConfiguration.loadConfiguration(getResource("lang_EN.yml"));

I was trying to make a language pack, with all translations saved in .yml to be read.

EDIT: Additional information: http://wiki.bukkit.org/Configuration_API_Reference#Paths

Example langPack.yml:

A:
  B: "Value"

Example Code:

String test = langPack_EN.get("A"); //Get B as Object
String test2 = langPack_EN.getString("A.B"); //Get "Value" as String

Is the dot affecting the 'path'? My assumption.