Don't return if deets were produced

src/internal/operations/backup.go

@@ -344,7 +344,7 @@ func (op *BackupOperation) do(
 		backupID,
 		op.incremental && canUseMetadata && canUsePreviousBackup,
 		op.Errors)
-	if err != nil {
+	if err != nil && (deets == nil || deets.Empty()) {
 		return nil, clues.Wrap(err, "persisting collection backups")
 	}
 

src/pkg/backup/details/details.go

@@ -401,6 +401,13 @@ func (b *Builder) Details() *Details {
 	return details
 }
 
+func (b *Builder) Empty() bool {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	return len(b.d.Entries) == 0
+}
+
 // --------------------------------------------------------------------------------
 // Details
 // --------------------------------------------------------------------------------