diff --git a/src/aeros_simulation/schema.py b/src/aeros_simulation/schema.py
index 74c5e40..32a23c2 100644
--- a/src/aeros_simulation/schema.py
+++ b/src/aeros_simulation/schema.py
@@ -119,4 +119,4 @@ class SimulationPagination(Pagination):
 
 class AhmMetricInput(BaseModel):
     target_simulation_id: str
-    baseline_simulation_id: Optional[str]
\ No newline at end of file
+    baseline_simulation_id: Optional[str] = Field(None)
\ No newline at end of file