为什么我的 CFN IAM 角色因 "Missing required field Action" 而失败?

Why is my CFN IAM role failing with "Missing required field Action"?

我的代码显然有一个动作。所以我假设它是一个格式错误。我知道这是一件愚蠢的事情,但我想不通。

Resources:
  LambdaExecRole:
    Type: AWS::IAM::Role
    Properties:
      Path: "/"
       AssumeRolePolicyDocument:
        Version: "2012-10-17"
        Statement:
         -
          Effect: Allow
           Principal:
            Action:
              - "sts:AssumeRole"
            Service:
              - "lambda.amazonaws.com"

行动需要与校长处于同一级别。