Getting following when ERROR message when I use let_once to declare variable that is used in request URL

[ps-ruby]

Failure/Error: raise TypeError.new("Unable to dump #{prefix}#{key} (#<#{val.class}>) in #{self.class.metadata[:location]}: #{$!}")

 TypeError:
   Unable to dump @controller (#<Api::V1::SalesUploadsController>) => @_request (#<ActionDispatch::Request>) => @env (#<Hash>) => ["rack.input"] (#<StringIO>) in ./spec/requests/sales_uploads/market_shares/create_spec.rb:85: no _dump_data is defined for class StringIO
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:139:in `rescue in find_dump_error'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:107:in `find_dump_error'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:129:in `block in find_dump_error'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:127:in `each_pair'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:127:in `rescue in find_dump_error'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:107:in `find_dump_error'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:123:in `block in find_dump_error'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:121:in `each'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:121:in `rescue in find_dump_error'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:107:in `find_dump_error'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:123:in `block in find_dump_error'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:121:in `each'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:121:in `rescue in find_dump_error'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:107:in `find_dump_error'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:91:in `block (2 levels) in __data'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:90:in `each'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:90:in `block in __data'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:89:in `each'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:89:in `rescue in __data'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:87:in `__data'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recorder.rb:88:in `record!'
 # /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/basic_helpers.rb:138:in `block in add_onceler_hooks!'
 # ------------------
 # --- Caused by: ---
 # TypeError:
 #   singleton can't be dumped
 #   /usr/local/rvm/gems/ruby-2.5.7/gems/once-ler-1.0.0/lib/onceler/recordable.rb:87:in `dump'