diff --git a/stacbuilder/builder.py b/stacbuilder/builder.py
index 26d09e6..e62110a 100644
--- a/stacbuilder/builder.py
+++ b/stacbuilder/builder.py
@@ -181,7 +181,9 @@ def is_known_asset_type(metadata: AssetMetadata) -> bool:
 
         known_assets = [a for a in assets if is_known_asset_type(a)]
         if not known_assets:
-            error_msg = "None of the assets in 'assets' is a known item type, not defined in collection configuration."
+            error_msg = ("None of the assets is defined in collection configuration. " +
+                         f"{[a.asset_type for a in assets]} not found in {list(self.item_assets_configs.keys())}")
+
             _logger.warning(error_msg)
             return None
 
diff --git a/stacbuilder/metadata.py b/stacbuilder/metadata.py
index cbadce7..ca2b729 100644
--- a/stacbuilder/metadata.py
+++ b/stacbuilder/metadata.py
@@ -16,7 +16,7 @@
 import datetime as dt
 import json
 from pathlib import Path
-from types import NoneType
+# from types import NoneType
 from typing import Any, Dict, List, Optional, Tuple, Union
 
 
@@ -34,6 +34,7 @@
 
 
 BoundingBoxList = List[Union[float, int]]
+NoneType = type(None)
 
 
 @dataclass