创建堆栈InvalidParameterValueException时出现A​​WS Cloudformation错误

Question

我正在尝试运行cloudformation脚本，其中我尝试使用EventSourceMapping资源将Lambda与运动学流绑定。我引入了导入值函数以在'EventSourceARN'属性中引用Kinesis流的ARN。当我尝试部署堆栈时，它会抛出：

1 validation error detected: Value null at 'startingPosition' failed to 
satisfy constraint: Member must not be null. (Service: AWSLambda; Status 
Code: 400; Error Code: InvalidParameterValueException; Request ID: 
a5b9a467-8f50-405c-a497-bde34fd1f0fd)

    Type: AWS::Lambda::EventSourceMapping
    Properties:
      EventSourceArn: 
         Fn::ImportValue: 
            !Sub "${Env}-NotificationLambdaArn"  
      FunctionName: !Join [ "-", [ Ref: Env, "dispatcher"] ]

命令：

aws cloudformation deploy --template-file templateFile.yaml --stack-name dispatcher-stack --paramter-overrides Env = develop