don't change non DateTime

gistfile1.rb

require 'rails_admin/config/fields/base'

module RailsAdmin
  module Config
    module Fields
      module Types
        class Datetime < RailsAdmin::Config::Fields::Base
          def value
            value_in_default_time_zone = bindings[:object].send(name)

            return nil if value_in_default_time_zone.nil?

            if value_in_default_time_zone.is_a?(DateTime)
              pacific_time_zone = ActiveSupport::TimeZone.new('US/Pacific')
              value_in_default_time_zone.in_time_zone(pacific_time_zone)
            else
              value_in_default_time_zone
            end
          end
        end
      end
    end
  end
end