Rack::Lint::Error => a header value must be a String or Array of Strings, but the value of 'content-type' is a NilClass about grape

[ericproulx]

I understand what's happening. Before #1922, content_type was taken from the base middleware which default to txt/plain.

# lib/grape/middleware/base.rb

def content_type
  content_type_for(env[Grape::Env::API_FORMAT] || options[:format]) || TEXT_HTML
end

Now, some test are now using rack_response instead of error! and this method will call content-type from the endpoint which will be nil if not set explicitely from header.

# lib/grape/dsl/inside_route.rb

def content_type(val = nil)
  if val
    header(Rack::CONTENT_TYPE, val)
  else
    header[Rack::CONTENT_TYPE]
  end
end

I don't think anyone is using rack_response in a rescue_from since its never been documented and I think we should
1 - remove the method from inside_route
2 - make the function private in lib/grape/middleware/error.rb, even though its not accessible anymore within rescue_from

[dblock]

Good plan. If no specs break we should be good.