diff --git a/flopy/mf6/mfpackage.py b/flopy/mf6/mfpackage.py
index 18bda23f19..c231998a17 100644
--- a/flopy/mf6/mfpackage.py
+++ b/flopy/mf6/mfpackage.py
@@ -1227,6 +1227,8 @@ def _add_missing_block_headers(self, repeating_dataset):
 
     def header_exists(self, key, data_path=None):
         if not isinstance(key, list):
+            if key is None:
+                return
             comp_key_list = [key]
         else:
             comp_key_list = key