I am writing a key value store API (like ODBC, just the interface, not the underlying store) in many different languages and while I do not want to transliterate the API between languages, I do not want for example to store a value from Java as a "null" and then read it in another language which does not support a concept of null. I'm not sure if I am explaining this so well, but its my first try :)
See :
http://stackoverflow.com/questions/2321650/is-this-api-too-simple
for the discussion about the key-value store API