Triage scapegoat warnings, part 1

Following the results of the scapegoat plugin at https://docs.google.com/spreadsheets/d/1z7xNMjx7VCJLCiHOHhTth7Hh4R0F6LwcGjEwCDzrCiM/edit#gid=767668040 and some initial triage, I'd like to address all of the valid instances of some classes of warning:

• BigDecimal double constructor
• Catching NPE
• Finalizer without super
• List.size is O
• Prefer Seq.empty
• Prefer Set.empty
• reverse.map instead of reverseMap
• Type shadowing
• Unnecessary if condition.
• Use .log1p
• Var could be val