field :fields and def fields=(fields) mixing up

[minsikzzang]

Issue

I've found issue in https://github.com/facebook/facebook-ruby-ads-sdk/blob/master/lib/facebook_ads/ad_object.rb#L48 when using insights creation api.

def initialize(attributes, *args)
   ...
   self.fields = fields + attributes.keys
   ...
end

above self.fields is usually calling def fields=(fields) below when there are no field: fields declared.

https://github.com/facebook/facebook-ruby-ads-sdk/blob/master/lib/facebook_ads/ad_object.rb#L96

But there is one place field: fields declared found below

https://github.com/facebook/facebook-ruby-ads-sdk/blob/master/lib/facebook_ads/ad_objects/ad_report_run.rb#L52

so when it goes to

self.fields = fields + attributes.keys

it tries to access below method with name=fields instead of calling instance method fields=

 def define_writer(name)
    define_method("#{name}=") do |val|
       changes[name] = val
       @fields.add(name.to_s)
    end
end

How to replicate this issue

FacebookAds::AdAccount.get('act_xxxxxx').insights(fields: 'ad_report_run').create(level: 'ad', fields: ['ad_id'])

This will throw exception
NoMethodError: undefined method `add' for nil:NilClass

Suggestion to fix

Just rename instance method def fields=(fields) to either def _fields=(fields) or more explicitly def response_fields=(fields)