Cleans ID array attributes before persisting with pair-tree Valkyrie Fedora.

app/models/hyrax/change_set.rb

@@ -45,5 +45,12 @@ class ChangeSet < Valkyrie::ChangeSet
     def self.for(resource)
       Hyrax::ChangeSet(resource.class).new(resource)
     end
+
+    def clean_id_fields_before_sync
+      id_fields = fields.keys.select { |k| k.include?('_id') }
+      multiple_id_fields_with_empties = id_fields.select { |f| fields[f].is_a?(Array) && fields[f].any?(&:empty?) }
+
+      multiple_id_fields_with_empties.each { |f| fields[f] = fields[f].reject(&:empty?) }
+    end
   end
 end

lib/hyrax/transactions/steps/save.rb

@@ -35,6 +35,7 @@ def call(change_set, user: nil)
             valid_future_date?(change_set.lease, 'lease_expiration_date') if change_set.respond_to?(:lease) && change_set.lease
             valid_future_date?(change_set.embargo, 'embargo_release_date') if change_set.respond_to?(:embargo) && change_set.embargo
             new_collections = changed_collection_membership(change_set)
+            change_set.clean_id_fields_before_sync
 
             unsaved = change_set.sync
             save_lease_or_embargo(unsaved)

spec/models/hyrax/change_set_spec.rb

@@ -5,7 +5,7 @@
 
 RSpec.describe Hyrax::ChangeSet do
   subject(:change_set) { described_class.for(resource) }
-  let(:resource)       { build(:hyrax_work) }
+  let(:resource)       { build(:hyrax_work, :with_default_admin_set) }
   let(:titles)         { ['comet in moominland', 'finn family moomintroll'] }
 
   it_behaves_like 'a Hyrax::ChangeSet'
@@ -34,6 +34,21 @@
     end
   end
 
+  describe '#clean_id_fields_before_sync' do
+    # NOTE: A pair-tree'ed Fedora storage scheme requires the elimiation of any
+    #   empty string values within a multivalued id attribute. If it passes along
+    #   to a parser that takes any value present in an array and converts it into
+    #   a Valkyrie::ID instance, Valkyrie's persister will attempt to pairtree that value.
+    it 'will eliminate empty string values from a change set' do
+      change_set.member_of_collection_ids = [""]
+
+      expect { change_set.clean_id_fields_before_sync }
+        .to change { change_set.member_of_collection_ids }
+        .from([""])
+        .to([])
+    end
+  end
+
   describe '#sync' do
     it 'applies changeset attributes' do
       change_set.title = titles