Rails 5 removes (https://github.com/rails/rails/commit/c414fc6) the where_values method that was present on relations, which is used in two places in Foreman:

app/models/filter.rb
72:    conditions = value ? limited.where_values.join(' AND ') : unlimited.where_values.map(&:to_sql).join(' AND ')

test/functional/application_controller_subclass_test.rb
200:      refute_nil actual_scope.where_values.index{|condition| condition.left.name == 'field1'}

The replacement is either to use the public/documented where_values_hash method or to introspect where_clause (but that's 5.0+ only and again, rather a private API).