Optimize SourceDatabase::getFormatsUsingTag(): avoid repeating the same queries

+++ b/src/Utility/SourceDatabase.php
@@ -153,6 +153,20 @@ class SourceDatabase {
+    $cid = implode(':', [
+      $tag,
+      is_string($field_names) ? $field_names : implode(',', $field_names),
+      $source_entity_type_id ?: 'any_entity_type',
+      $source_bundle ?: 'any_bundle',
+    ]);

I know that it's an edge case, but I would rather see an array filter here instead of using default values when $source_entity_type_id and/or $source_bundle are empty.