diff --git a/jwst/datamodels/container.py b/jwst/datamodels/container.py
index 2a560f3aa0..5b6baa71c8 100644
--- a/jwst/datamodels/container.py
+++ b/jwst/datamodels/container.py
@@ -138,6 +138,8 @@ def __init__(self, init=None, asn_exptypes=None, asn_n_members=None,
 
         self._memmap = kwargs.get("memmap", False)
 
+        if init is None:
+            init = []
         if isinstance(init, list):
             self._models = []
             for item in init: