I don't see the point of having a generic type parameter on the StrLookup class, if it's not used anywhere. No method / field in StrLookup references this type parameter. IntelliJ IDEA itself reports a warning: "Type parameter 'V' is never used". Moreover, Java generics are not reified, so there is no reliable way to access the type parameter at runtime (and I don't see the point of doing that anyway...).
While the Javadoc tries to clarify the purpose of a StrLookup, the unused type parameter is still confusing, and the client code has to un-necessarily specify type parameters. For example, I have to write:
My best guess is that this type parameter was added when commons-lang was generified, because StringLookup.mapLookup() takes a generified Map. Doing this is not really needed, though: we could remove the <V> type parameter everywhere, and replace the StrLookup.mapLookup()'s Map<String, V> with a Map<String, ?> (which is the same as Map<String, ? extends Object>, but shorter).
I guess it's too late to change this now, due to backward compatibility... But I thought I'd comment just in case it's still possible.