fix: patch bad runtime error related to memory access (SandboxReturn.…

…agent_stateis Optional, so not guaranteed to exist)

letta/agent.py

@@ -237,8 +237,8 @@ def execute_tool_and_persist_state(self, function_name: str, function_args: dict
                 )
                 function_response, updated_agent_state = sandbox_run_result.func_return, sandbox_run_result.agent_state
                 assert orig_memory_str == self.agent_state.memory.compile(), "Memory should not be modified in a sandbox tool"
-
-                self.update_memory_if_change(updated_agent_state.memory)
+                if updated_agent_state is not None:
+                    self.update_memory_if_change(updated_agent_state.memory)
         except Exception as e:
             # Need to catch error here, or else trunction wont happen
             # TODO: modify to function execution error