QueryBuilder has generics, but those are never used: all call sites use
`QueryBuilder<?>`. Only `AbstractQueryBuilder` needs generics so that the base
class can contain a default implementation for setters that returns `this`.
The available memory metric was always set to `0` since 2.0.beta1 (bug). was left behind but never set. Turns out the section wasn't that useful, as it would only output the total memory available throughout all nodes in the cluster. We decided to remove the section then.
