Bulk Upload "Append" fails with `IndexError('list index out of range',)`

[mradamcox]

User Story

In fixing another issue with bulk upload, I found that I was unable to load the attached file with Append as a configuration in step 2. The printout in the console is

[01/Jul/2019 14:14:18] "POST /bulk-upload/validate HTTP/1.1" 200 108
operation: validate
  suboperation: write_arches_file
package: eamena
IndexError('list index out of range',)
[01/Jul/2019 14:14:18] "POST /bulk-upload/validate HTTP/1.1" 500 21258

v2.2_E27_UPLOAD TEMPLATE_Heritage Place_2.xlsx

This error should be handled better, because currently the loading spinning wheel just keeps spinning........