refactor: make code simpler

Signed-off-by: -LAN- <laipz8200@outlook.com>

api/dify_graph/runtime/graph_runtime_state.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 import importlib
 import json
 from collections.abc import Mapping, Sequence
-from contextlib import AbstractContextManager
+from contextlib import AbstractContextManager, nullcontext
 from copy import deepcopy
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, Any, ClassVar, Protocol
@@ -235,7 +235,7 @@ class GraphRuntimeState:
         self._response_coordinator = response_coordinator
         # Application code injects this when worker threads must restore request
         # or framework-local state. It is intentionally excluded from snapshots.
-        self._execution_context = execution_context
+        self._execution_context = execution_context if execution_context is not None else nullcontext()
         self._pending_response_coordinator_dump: str | None = None
         self._pending_graph_execution_workflow_id: str | None = None
         self._paused_nodes: set[str] = set()
@@ -335,12 +335,12 @@ class GraphRuntimeState:
         return self._response_coordinator
 
     @property
-    def execution_context(self) -> AbstractContextManager[object] | None:
+    def execution_context(self) -> AbstractContextManager[object]:
         return self._execution_context
 
     @execution_context.setter
     def execution_context(self, value: AbstractContextManager[object] | None) -> None:
-        self._execution_context = value
+        self._execution_context = value if value is not None else nullcontext()
 
     # ------------------------------------------------------------------
     # Scalar state