Ruby on Rails error when parsing XML - ruby-on-rails

Question

I get this error now when parsing XML's using my Ruby on Rails server:
ERROR -- : exception while processing events: undefined method
`content' for nil:NilClass Backtrace
-- /var/www/distribution/distribution-server/app/models/upload_action.rb:23:in `block in upload'
-- /var/www/distribution/distribution-server/app/models/upload_action.rb:14:in `each'
-- /var/www/distribution/distribution-server/app/models/upload_action.rb:14:in `upload'
-- /var/www/distribution/distribution-server/app/services/run_listener.rb:8:in `block in start'
The relevant code:
def self.upload(xml_files)
actions = []
xml_files.each do |xml_file|
if File.exist?(xml_file)
doc = File.open(xml_file) { |f| Nokogiri::XML(f) }
action = UploadAction.new
action.file_name = [doc.xpath("//field[#index='103']").first.content]
action.content_provider_name = doc.xpath("//field[#index='45']").first.content
action.content_provider_title = doc.xpath("//field[#index='24']").first.content
action.created_date = doc.xpath("//field[#index='13']").first.content.to_date
action.credit_line = doc.xpath("//field[#index='91']").first.content
The error occurs on the third line of 'action', action.content_provider_name. All required fields in the XML are correctly filled out. If I change doc.xpath("//field[#index='45']").first.content to a string, like 'Example String', then action.content_provider_title has the error.
Edit
Partial Example of XML Fields:
`<metadata>
<field index="24" type="picklist"
name="content_provider_title">title</field>
<field index="45" type="picklist"
name="content_provider_name">name</field>
<field index="79" type="text" name="Monitor State">Restored</field>
<field index="81" type="checkbox" name="Confirm Delete">false</field>
</metadata>`

Answer 1

Depending on the version of Rails you use, you can change the following line to one of the options below it:
action.file_name = [doc.xpath("//field[#index='103']").first.content]
Updating to:
action.file_name = [doc.xpath("//field[#index='103']").first&.content]
# or
action.file_name = [doc.xpath("//field[#index='103']").first.try(:content)]
Both of these options protect against NilClass errors. If you don't necessarily need value for action.file_name, this will fix the error.
Otherwise, it's a case of ensuring the selector (doc.xpath("//field[#index='103']")) is definitely correct (it seems to be, as you're not getting an error calling first) and, if so, that there is definitely data in the array it returns.
Hope that helps - let me know if you've any questions.