The CoreMap key for getting the syntactic dependencies of a sentence.
Note: this is no longer used, but it appears in sentences cached during KBP 2010.
This key is typically set on sentence annotations.
Returns the type associated with this annotation. This method must
return the same class type as its value type parameter. It feels like
one should be able to get away without this method, but because Java
erases the generic type signature, that info disappears at runtime.