fix(memory): use explicit None checks and remove unnecessary Optional type

- Replace truthiness checks with 'is not None' for data.message in graph_data and community_graph endpoints to handle empty string correctly
- Remove Optional wrapper from GraphStatistics.edge_types since it already has a default_factory

api/app/controllers/user_memory_controllers.py

@@ -350,7 +350,7 @@ async def get_graph_data_api(
         )
 
         # 检查是否有错误消息
-        if data.message and data.statistics.total_nodes == 0:
+        if data.message is not None and data.statistics.total_nodes == 0:
             api_logger.warning(f"图数据查询返回空结果: {data.message}")
             return success(data=data.model_dump(), msg=data.message)
 
@@ -394,7 +394,7 @@ async def get_community_graph_data_api(
             message=result.get("message"),
         )
 
-        if data.message and data.statistics.total_nodes == 0:
+        if data.message is not None and data.statistics.total_nodes == 0:
             api_logger.warning(f"社区图谱查询返回空结果: {data.message}")
             return success(data=data.model_dump(), msg=data.message)
 

api/app/schemas/user_memory_schema.py

@@ -99,7 +99,7 @@ class GraphStatistics(BaseModel):
     total_nodes: int = Field(0, description="节点总数")
     total_edges: int = Field(0, description="边总数")
     node_types: Dict[str, int] = Field(default_factory=dict, description="各节点类型数量")
-    edge_types: Optional[Dict[str, int]] = Field(default_factory=dict, description="各边类型数量")
+    edge_types: Dict[str, int] = Field(default_factory=dict, description="各边类型数量")
 
 
 class GraphData(BaseModel):