lib/contentful/content_type.rb
def field_for(field_id)
      fields.detect { |f| Support.snakify(f.id) == Support.snakify(field_id) }
    end
def field_for(field_id)
      fields.detect { |f| Support.snakify(f.id) == Support.snakify(field_id) }
    end
Field definition for field