NoMethodError (undefined method `[]' for nil:NilClass) after updating to 0.34.1

[charger]

After updating gem to 0.34.0 or 0.34.1 I got an error when visit http://localhost:3000/api/swagger_doc

NoMethodError (undefined method `[]' for nil:NilClass):
  
grape (1.2.5) lib/grape/router.rb:163:in `cascade?'
grape (1.2.5) lib/grape/router.rb:95:in `transaction'
grape (1.2.5) lib/grape/router.rb:72:in `identity'
...

The code in gem:

    def cascade?(response)
      response && response[1][Grape::Http::Headers::X_CASCADE] == 'pass'
    end

response[1] is nil

Which additional information I can provide?

[LeFnord]

is it related to #767 ?

[charger]

It's hard to say if these two issues are related. They are both actual but occur in different places.
The issue in question occurs if I update grape-swagger to 0.34:

NoMethodError (undefined method `[]' for nil:NilClass):
grape (1.2.5) lib/grape/router.rb:163:in `cascade?'

I don't encountered the #767, but if I add target_class: ::Map::API to my add_swagger_documentation I got error even using old grape-swagger 0.33:

Uncaught exception: undefined method `unshift' for nil:NilClass
~/.rvm/gems/ruby-2.6.3/gems/grape-swagger-0.33.0/lib/grape-swagger.rb:40:in `block in combine_routes'

[hgeorgilas]

Got the same error, I think it's related to ruby-grape/grape #1966.
But gemspec file won't let me upgrade to grape 1.3.0

[LeFnord]

yeap the failure is rack based → a workaround is to fix it to version 2.0.8, see also this grape#1980

[LeFnord]

had to freeze the rack version for the moment → 0.34.2

updating to grape >= 1.3.0 will be possible with the next release, see: #768 (comment)