Missing field b error

[jeremyf]

When running an importer with the following Bulkrax parser configuration, we encountered a "Missing field b error":

config.field_mappings['Bulkrax::CsvParser'] = {
  'bulkrax_identifier' => { from: ['source_identifier'], source_identifier: true, search_field: 'bulkrax_identifier_tesim' },
  'children' => { from: ['children'], split: /\s*[;|]\s*/, related_children_field_mapping: true },
  'parents' => { from: ['parents'], split: /\s*[;|]\s*/, related_parents_field_mapping: true }
}