diff --git a/src/ifcopenshell-python/ifcopenshell/api/cost/calculate_cost_item_resource_value.py b/src/ifcopenshell-python/ifcopenshell/api/cost/calculate_cost_item_resource_value.py
index fcdd4084ce..e1eb12db85 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/cost/calculate_cost_item_resource_value.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/cost/calculate_cost_item_resource_value.py
@@ -101,12 +101,11 @@ def calculate_cost_item_resource_value(file: ifcopenshell.file, cost_item: ifcop
 
     for resource in resources:
         cost, unit = ifcopenshell.util.resource.get_cost(resource)
-        # TODO: cost is never None because get_cost always returns a float.
         if cost is None:
             # Concept to standardise - Not defined in schema, but this makes manual scheduling of resources 10x faster and less duplicate data.
             parent_cost = ifcopenshell.util.resource.get_parent_cost(resource)
-            assert parent_cost
-            cost, unit = parent_cost
+            if parent_cost:
+                cost, unit = parent_cost
         quantity = ifcopenshell.util.resource.get_quantity(resource)
         if cost is None:
             continue
diff --git a/src/ifcopenshell-python/ifcopenshell/util/resource.py b/src/ifcopenshell-python/ifcopenshell/util/resource.py
index 2df15e7a63..f518a09125 100644
--- a/src/ifcopenshell-python/ifcopenshell/util/resource.py
+++ b/src/ifcopenshell-python/ifcopenshell/util/resource.py
@@ -139,22 +139,18 @@ def get_nested_resources(resource: ifcopenshell.entity_instance) -> list[ifcopen
     return [object for rel in resource.IsNestedBy or [] for object in rel.RelatedObjects]
 
 
-def get_cost(resource: ifcopenshell.entity_instance) -> tuple[float, Union[str, None]]:
-    base_costs = getattr(resource, "BaseCosts", [])
-    costs = (
-        [ifcopenshell.util.cost.calculate_applied_value(resource, cost_value) for cost_value in base_costs]
-        if base_costs
-        else []
-    )
-    cost = sum(costs)
-    unit_basis = (
-        next((cost_value.UnitBasis for cost_value in base_costs if cost_value.UnitBasis), None) if base_costs else None
-    )
-    unit = (
-        unit_basis.UnitComponent.Name
-        if unit_basis and unit_basis.UnitComponent.is_a("IfcConversionBasedUnit")
-        else None
-    )
+def get_cost(resource: ifcopenshell.entity_instance) -> tuple[Union[float, None], Union[str, None]]:
+    """Get cost data for IfcConstructionResource.
+
+    :return: a tuple of cost and unit.
+    """
+    cost, unit = None, None
+    if base_costs := resource.BaseCosts:
+        costs = [ifcopenshell.util.cost.calculate_applied_value(resource, cost_value) for cost_value in base_costs]
+        cost = sum(costs)
+        unit_basis = next((unit_basis for cost_value in base_costs if (unit_basis := cost_value.UnitBasis)), None)
+        if unit_basis and (unit_component := unit_basis.UnitComponent).is_a("IfcConversionBasedUnit"):
+            unit = unit_component.Name
     return cost, unit
 
 
@@ -167,7 +163,7 @@ def get_quantity(resource: ifcopenshell.entity_instance) -> float:
     return 1.0 if quantity is None else quantity[3]
 
 
-def get_parent_cost(resource: ifcopenshell.entity_instance) -> Union[tuple[float, Union[str, None]], None]:
+def get_parent_cost(resource: ifcopenshell.entity_instance) -> Union[tuple[Union[float, None], Union[str, None]], None]:
     if not (nests := resource.Nests):
         return
     else: