carrierwave: when migrating, create an empty blob if file is missing

app/services/carrierwave_active_storage_migration_service.rb

@@ -79,7 +79,7 @@ class CarrierwaveActiveStorageMigrationService
 
     ActiveStorage::Blob.create(
       filename: filename || uploader.filename,
-      content_type: uploader.content_type,
+      content_type: content_type,
       byte_size: uploader.size,
       checksum: checksum(uploader),
       created_at: created_at,
@@ -87,6 +87,20 @@ class CarrierwaveActiveStorageMigrationService
     )
   end
 
+  def make_empty_blob(uploader, created_at, filename: nil)
+    content_type = uploader.content_type || 'text/plain'
+
+    blob = ActiveStorage::Blob.build_after_upload(
+      io: StringIO.new('File not found when migrating from CarrierWave.'),
+      filename: filename || uploader.filename,
+      content_type: content_type || 'text/plain',
+      metadata: { virus_scan_result: ActiveStorage::VirusScanner::SAFE }
+    )
+    blob.created_at = created_at
+    blob.save!
+    blob
+  end
+
   def checksum(uploader)
     hex_to_base64(uploader.file.send(:file).etag)
   end

app/services/piece_justificative_to_champ_piece_jointe_migration_service.rb

@@ -75,12 +75,18 @@ class PieceJustificativeToChampPieceJointeMigrationService
   end
 
   def convert_pj_to_champ!(pj, champ)
-    blob = make_blob(pj)
+    actual_file_exists = pj.content.file.send(:file)
+    if actual_file_exists
+      blob = make_blob(pj)
 
-    # Upload the file before creating the attachment to make sure MIME type
-    # identification doesn’t fail.
-    storage_service.copy_from_carrierwave_to_active_storage!(pj.content.path, blob)
-    attachment = storage_service.make_attachment(champ, 'piece_justificative_file', blob)
+      # Upload the file before creating the attachment to make sure MIME type
+      # identification doesn’t fail.
+      storage_service.copy_from_carrierwave_to_active_storage!(pj.content.path, blob)
+      attachment = storage_service.make_attachment(champ, 'piece_justificative_file', blob)
+
+    else
+      make_empty_blob(pj)
+    end
 
     # By reloading, we force ActiveStorage to look at the attachment again, and see
     # that one exists now. We do this so that, if we need to roll back and destroy the champ,
@@ -112,4 +118,8 @@ class PieceJustificativeToChampPieceJointeMigrationService
   def make_blob(pj)
     storage_service.make_blob(pj.content, pj.updated_at.iso8601, filename: pj.original_filename)
   end
+
+  def make_empty_blob(pj)
+    storage_service.make_empty_blob(pj.content, pj.updated_at.iso8601, filename: pj.original_filename)
+  end
 end