[Bug]: bug in DictDialogAgent when use_memory = False

[wujiren]

AgentScope is an open-source project. To involve a broader community, we recommend asking your questions in English.

Describe the bug
In DictDialogAgent , if you set use_memory = False, the source code in reply() method will raise error

        self.memory.add(
            Msg(self.name, self.parser.to_memory(res.parsed), "assistant"),
        )

Reason: self.memory is None

To Reproduce
Steps to reproduce the behavior:

1. source code

import agentscope
from agentscope.agents import DictDialogAgent
from agentscope.message import Msg
from agentscope.parsers import MarkdownJsonDictParser

if __name__ == "__main__":
    agentscope.init(model_configs="yor configs", logger_level="DEBUG")
    parser = MarkdownJsonDictParser(content_hint={"reply": "your reply"})
    agent = DictDialogAgent(
        name="Agent",
        sys_prompt="you are an agent\n{content_hint}",
        model_config_name="your config name",
        use_memory=False, // this is when the error will be raised
    )
    agent.set_parser(parser)
    x = agent(Msg("user", "I'm testing you"))

Expected behavior
nothing

Error messages

Traceback (most recent call last):
  File "/Volumes/work/workspace/llm/writing/test_error.py", line 18, in <module>
    x = agent(Msg("user", "I'm testing you"))
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jirenwu/anaconda3/envs/chatgpt/lib/python3.11/site-packages/agentscope/agents/agent.py", line 296, in __call__
    res = self.reply(*args, **kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jirenwu/anaconda3/envs/chatgpt/lib/python3.11/site-packages/agentscope/agents/dict_dialog_agent.py", line 111, in reply
    self.memory.add(
    ^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'add'

Environment (please complete the following information):

• AgentScope Version: ['0.0.6alpha3]
• Python Version: [3.11]
• OS: [macoss]

Additional context
maybe you should:

    if self.memory: 
        self.memory.add(
            Msg(self.name, self.parser.to_memory(res.parsed), "assistant"),
        )

[DavdGao]

Thanks for your reporting, we will fix it as soon as possible.