There is no inconsistency. Note the following sentence in http://www.eigenbase.org/wiki/index.php/LucidDbFlatFileWrapper
> Note that empty quotes ("") represents the empty string, while a completely empty value () represents a null.
And null is a legal numeric value, whereas empty string is not (according to the rules for CAST, which is what we use to arbitrate the interpretation of flatfile values).
In that document, I have added a link to this bug as clarification.