[Minor] Fix a typo of type parameter in JavaUtils.scala

In JavaUtils.scala, thare is a typo of type parameter. In addition, the type information is removed at the time of compile by erasure.

This issue is really minor so I don't  file in JIRA.
Should this really be `A` to express the relation to the generic bound? although `underlying` must already have keys of type `A` already. It just looks like that was the intent.