Error loading pghero page

[edbond]

database.yml contains only one production: key

gem 'rails', '4.2.10'

pghero mounted as
config/routes.rb

  authenticate :admin do
    mount PgHero::Engine, at: "/pghero"
  end

Log:

I, [2018-09-14T05:45:53.893343 #9815]  INFO -- : Processing by PgHero::HomeController#index as HTML
E, [2018-09-14T05:45:53.896241 #9815] ERROR -- : [ReplicaPools] Error during #select_all: undefined method `empty?' for nil:NilClass
E, [2018-09-14T05:45:53.896298 #9815] ERROR -- : [ReplicaPools] Current Connection: ActiveRecord::Base
E, [2018-09-14T05:45:53.896367 #9815] ERROR -- : [ReplicaPools] Current Pool Name: default
E, [2018-09-14T05:45:53.896430 #9815] ERROR -- : [ReplicaPools] Current Pool Members: [ReplicaPools::DefaultStocktalk(abstract)]
E, [2018-09-14T05:45:53.896477 #9815] ERROR -- : [ReplicaPools] leader Depth: 0
E, [2018-09-14T05:45:53.896838 #9815] ERROR -- : [ReplicaPools] Error during #cache_sql: undefined method `empty?' for nil:NilClass
E, [2018-09-14T05:45:53.896887 #9815] ERROR -- : [ReplicaPools] Current Connection: ActiveRecord::Base
E, [2018-09-14T05:45:53.896927 #9815] ERROR -- : [ReplicaPools] Current Pool Name: default
E, [2018-09-14T05:45:53.896976 #9815] ERROR -- : [ReplicaPools] Current Pool Members: [ReplicaPools::DefaultStocktalk(abstract)]