diff --git a/python/ngen_conf/src/ngen/config/cfe.py b/python/ngen_conf/src/ngen/config/cfe.py
index 7584d449..13efe1b8 100644
--- a/python/ngen_conf/src/ngen/config/cfe.py
+++ b/python/ngen_conf/src/ngen/config/cfe.py
@@ -16,7 +16,7 @@ class CFEParams(BaseModel):
 class CFE(BMIC):
     """A BMIC implementation for the CFE ngen module
     """
-    model_params: CFEParams = {}
+    model_params: Optional[CFEParams]
     main_output_variable: str = 'Q_OUT'
     registration_function: str = "register_bmi_cfe"
     #NOTE aliases don't propagate to subclasses, so we have to repeat the alias
diff --git a/python/ngen_conf/src/ngen/config/topmod.py b/python/ngen_conf/src/ngen/config/topmod.py
index 324c84f5..0266e505 100644
--- a/python/ngen_conf/src/ngen/config/topmod.py
+++ b/python/ngen_conf/src/ngen/config/topmod.py
@@ -15,7 +15,7 @@ class TopmodParams(BaseModel):
 class Topmod(BMIC):
     """A BMIC implementation for the Topmod ngen module
     """
-    model_params: TopmodParams = {}
+    model_params: Optional[TopmodParams]
     main_output_variable: str = 'Qout'
     registration_function: str = "register_bmi_topmodel"
     #NOTE aliases don't propagate to subclasses, so we have to repeat the alias