```ruby
module CaTissue
  # Declares the classes modified for migration.
  shims Participant, SpecimenCollectionGroup

  class Participant::Clinical::Duration
    # Makes a non-PHI date field from the year input value.
    #
    # @param [Integer] year the diagnosis year
    # @param row (see CaRuby::Migratable#migrate)
    # @return [Date] July 2 of the given year
    def migrate_start_date(year, row)
      Date.new(year, 7, 2)
    end
  end

  class SpecimenCollectionGroup
  end
end```

Remove extraneous empty SCG class def.
user
```ruby
module CaTissue
  # Declares the classes modified for migration.
  shims Participant, SpecimenCollectionGroup

  class Participant::Clinical::Duration
    # Makes a non-PHI date field from the year input value.
    #
    # @param [Integer] year the diagnosis year
    # @param row (see CaRuby::Migratable#migrate)
    # @return [Date] July 2 of the given year
    def migrate_start_date(year, row)
      Date.new(year, 7, 2)
    end
  end
end```
assistant