fix:settings changes detection issue with empty array

[kiyohara]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Related Issue	-
Need Doc update	no

Describe your change

If you set customRanking as an empty Array, like below, Algolia understands that you set the customRanking as null.

class Product < ActiveRecord::Base
  include AlgoliaSearch

  algoliasearch do
    customRanking [] # emptry Array
  end
end

As a result, the index setting API ( /1/indexes/%s/settings?getVersion=1 ) returns setting information like below.
customRanking is nil.

=> {
 "minWordSizefor1Typo"=>4,
 "minWordSizefor2Typos"=>8,
 "hitsPerPage"=>20,
 "maxValuesPerFacet"=>100,
 "version"=>1,
 # snip
 "customRanking"=>nil # API's response, raw JSON, is "customRanking":null
}

This behavior is natural and understandable.
However, the settings changes checking function does not handle this difference correctly.
So, I add an additional compare logic to the function, especially [] and nil comparing using blank? method.

What problem is this fixing?

If you set customRanking ( or any other attributes ) as an empty Array , a useless index setting update API will be called when you use the search function.
It's heavy and blocking(synchronous) API calling, so your search function might be timed out.

[kiyohara]

Any specs error has been occurred caused by Invalid Application-ID or API key (Algolia::AlgoliaHttpError).
I guess it's a permission issue I can't solve.
Is there anything I can do?

[DevinCodes]

Thank you for the PR @kiyohara ! 🙇‍♂️

The CI is failing because environment variables aren't available in our CI when ran from a fork. I've restarted it so that the credentials get loaded, it's looking good! 🙂