Uploading a roster with header row produces NPE

[s-edwards]

If an uploaded roster (on the course home page, roster tab) includes a header row and you check the corresponding box, the code fails with:

undefined method `downcase' for nil:NilClass

The relevant stack trace:

/home/codeworkout/rails/releases/20210412123406/app/controllers/course_enrollments_controller.rb:55:in block in roster_upload' /usr/local/rvm/rubies/ruby-2.6.3/lib/ruby/2.6.0/csv/parser.rb:1078:in emit_row'
/usr/local/rvm/rubies/ruby-2.6.3/lib/ruby/2.6.0/csv/parser.rb:827:in block in parse_quotable_loose' /usr/local/rvm/rubies/ruby-2.6.3/lib/ruby/2.6.0/csv/parser.rb:31:in block in each_line'
/usr/local/rvm/rubies/ruby-2.6.3/lib/ruby/2.6.0/csv/parser.rb:28:in each_line' /usr/local/rvm/rubies/ruby-2.6.3/lib/ruby/2.6.0/csv/parser.rb:28:in each_line'
/usr/local/rvm/rubies/ruby-2.6.3/lib/ruby/2.6.0/csv/parser.rb:779:in parse_quotable_loose' /usr/local/rvm/rubies/ruby-2.6.3/lib/ruby/2.6.0/csv/parser.rb:303:in parse'
/usr/local/rvm/rubies/ruby-2.6.3/lib/ruby/2.6.0/csv.rb:1236:in each' /usr/local/rvm/rubies/ruby-2.6.3/lib/ruby/2.6.0/csv.rb:1236:in each'
/usr/local/rvm/rubies/ruby-2.6.3/lib/ruby/2.6.0/csv.rb:681:in parse' /home/codeworkout/rails/releases/20210412123406/app/controllers/course_enrollments_controller.rb:38:in roster_upload'