diff --git a/gollm/entities.py b/gollm/entities.py
index 07a2cee..8c10089 100644
--- a/gollm/entities.py
+++ b/gollm/entities.py
@@ -17,7 +17,7 @@ class ConfigureModelDataset(BaseModel):
 
 class ModelCardModel(BaseModel):
     amr: str  # expects AMR in a stringified JSON object
-    research_paper: str
+    research_paper: str = None
 
 
 class ModelCompareModel(BaseModel):