AttributeError:在Python语言中将代码行转换为函数时，“NoneType”对象没有属性“exec_command”

import paramiko

def execute_command():
    try:
        # SSH连接配置
        ssh = paramiko.SSHClient()
        ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
        ssh.connect('hostname', port=22, username='username', password='password')
        
        # 执行远程命令
        stdin, stdout, stderr = ssh.exec_command('command')
        
        # 检查返回值是否为None
        if stdout is not None:
            # 处理命令输出
            print(stdout.read().decode())
        else:
            print('Command execution failed.')
        
        # 关闭SSH连接
        ssh.close()
    except paramiko.AuthenticationException as e:
        print('Authentication failed:', str(e))
    except paramiko.SSHException as e:
        print('SSH connection failed:', str(e))
    except paramiko.BadHostKeyException as e:
        print('Host key could not be verified:', str(e))
    except Exception as e:
        print('An error occurred:', str(e))

execute_command()