[Bug]:使用 OllamaChatModel 时无入参工具调用失败

[wozai604]

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Describe the bug
使用 OllamaChatModel 通过本地模型进行一个无入参工具的调用失败，仅把模型改为OpenAIChatModel 则能成功。

To Reproduce
Steps to reproduce the behavior:

package io.agentscope.examples.quickstart;

import io.agentscope.core.ReActAgent;
import io.agentscope.core.formatter.ollama.OllamaChatFormatter;
import io.agentscope.core.memory.InMemoryMemory;
import io.agentscope.core.model.OllamaChatModel;
import io.agentscope.core.tool.Tool;
import io.agentscope.core.tool.Toolkit;
import java.io.IOException;
import java.time.LocalDateTime;

public class LocalToolCallingExample {
    public static void main(String[] args) throws IOException {
        // 注册工具
        Toolkit toolkit = new Toolkit();
        toolkit.registerTool(new ExampleTool());
        // 定义模型
        //                OpenAIChatModel model = OpenAIChatModel.builder()
        //                        .modelName("qwen3:0.6b")
        //                        .stream(false)
        //                        .baseUrl("http://127.0.0.1:11434")
        //                        .formatter(new OpenAIChatFormatter())
        //                        .build();
        OllamaChatModel model =
                OllamaChatModel.builder()
                        .modelName("qwen3:0.6b")
                        .baseUrl("http://127.0.0.1:11434")
                        .formatter(new OllamaChatFormatter())
                        .build();
        // 定义智能体
        ReActAgent agent =
                ReActAgent.builder()
                        .name("David")
                        .sysPrompt("你是一个名为逗你玩的智能体，请不要从上下文中找答案。")
                        .memory(new InMemoryMemory())
                        .model(model)
                        .toolkit(toolkit)
                        .build();

        //        Msg msg = Msg.builder()
        //                .name("张三")
        //                .textContent("现在是几点了？")
        //                .role(MsgRole.USER)
        //                .build();
        //
        //        Msg response = agent.call(msg).block();
        //        System.out.println(response);
        ExampleUtils.startChat(agent);
    }

    public static class ExampleTool {
        @Tool(description = "获取当前时间")
        public String getTime() {
            System.out.println("=========》 getTime ");
            return LocalDateTime.now().toString();
        }
    }
}

Error messages
io.agentscope.core.tool.ToolExecutor Line:157 - Parameter validation failed for tool 'getTime': Schema validation error: argument "content" is null
实际输出

{
	"model": "qwen3:0.6b",
	"messages": [{
		"role": "system",
		"content": "你是一个名为逗你玩的智能体，请不要从上下文中找答案。"
	}, {
		"role": "user",
		"content": "你通过工具调用的结果告诉我现在几点了。"
	}, {
		"role": "assistant",
		"tool_calls": [{
			"function": {
				"name": "getTime",
				"arguments": {}
			}
		}]
	}, {
		"role": "tool",
		"content": "Error: Parameter validation failed for tool 'getTime': Schema validation error: argument \"content\" is null\nPlease correct the parameters and try again.",
		"tool_call_id": "666bb26d-6bdf-4bd4-9a6c-5ad6346ccbe9",
		"name": "getTime"
	}],
	"stream": true,
	"tools": [{
		"type": "function",
		"function": {
			"name": "getTime",
			"description": "获取当前时间",
			"parameters": {
				"type": "object",
				"properties": {}
			}
		}
	}],
	"options": {}
}

Environment (please complete the following information):

• AgentScope-Java Version: [e.g. 1.0.7, check your pom.xml dependency version or run mvn dependency:tree | grep agentscope-parent:pom(only mac/linux)]
• Java Version:17
• OS:windows