diff --git a/code/backend/nest_backend/database/tables/Repository.py b/code/backend/nest_backend/database/tables/Repository.py
index 7484202..669c9d6 100644
--- a/code/backend/nest_backend/database/tables/Repository.py
+++ b/code/backend/nest_backend/database/tables/Repository.py
@@ -22,5 +22,5 @@ class Repository(Base.Model):
     uses = Base.relationship("Uses", back_populates="repository")
 
     def to_json(self):
-        return {"id": self.id, "name": self.name, "start": self.start.isoformat(), "isActive":self.isActive,
-                "end":self.end.isoformat(),"owner": self.owner.to_json()}
+        return {"id": self.id, "name": self.name, "start": (self.start.isoformat() if self.start is not None else ""), "isActive":self.isActive,
+                "end":(self.end.isoformat() if self.end is not None else ""),"owner": self.owner.to_json()}