diff --git a/app/infrastructure/repositories.py b/app/infrastructure/repositories.py
index a023c68..22344f2 100644
--- a/app/infrastructure/repositories.py
+++ b/app/infrastructure/repositories.py
@@ -1065,21 +1065,21 @@ class AgentRepository:
         }
 
     async def get_by_user(self, user_id: str, port: str | None = None) -> list[dict]:
-        if not port:
+        if port is None:
             return []
         stmt = select(Agent).where(Agent.user_id == user_id, Agent.port == port)
         rows = await self.session.scalars(stmt.order_by(Agent.created_at))
         return [self._to_dict(a) for a in rows]
 
     async def get(self, agent_id: str, user_id: str, port: str | None = None) -> dict | None:
-        if not port:
+        if port is None:
             return None
         stmt = select(Agent).where(Agent.id == agent_id, Agent.user_id == user_id, Agent.port == port)
         a = await self.session.scalar(stmt)
         return self._to_dict(a) if a else None
 
     async def count_by_user(self, user_id: str, port: str | None = None) -> int:
-        if not port:
+        if port is None:
             return 0
         stmt = select(Agent.id).where(Agent.user_id == user_id, Agent.port == port)
         return len(list(await self.session.scalars(stmt)))
@@ -1114,7 +1114,7 @@ class AgentRepository:
         return self._to_dict(a)
 
     async def update(self, agent_id: str, user_id: str, fields: dict, port: str | None = None) -> dict | None:
-        if not port:
+        if port is None:
             return None
         stmt = select(Agent).where(Agent.id == agent_id, Agent.user_id == user_id, Agent.port == port)
         a = await self.session.scalar(stmt)
@@ -1134,7 +1134,7 @@ class AgentRepository:
         return self._to_dict(a)
 
     async def delete(self, agent_id: str, user_id: str, port: str | None = None) -> bool:
-        if not port:
+        if port is None:
             return False
         stmt = select(Agent).where(Agent.id == agent_id, Agent.user_id == user_id, Agent.port == port)
         a = await self.session.scalar(stmt)