Fn :: Sub中的嵌套Fn :: ImportValue不适用于SAM模板

Description: 我正在尝试定义无服务器API资源 . 但是在使用函数ImportValue定义swagger规范文件的位置时遇到了麻烦 .

Steps to reproduce the issue: 我无法在Location中定义具有嵌套函数 ImportValue 的 AWS::Serverless::Api 资源 . 我尝试过以下三种方法，但都没有 .

注意：堆栈参数已正确定义，并且存在来自其他堆栈的导出值 . 由于简洁的原因，没有在这里显示它们 .

ApiGatewayApi:
    Type: AWS::Serverless::Api
    Properties:
        Name: !Sub ${AWS::StackName}-API
        StageName: !Ref ApiGatewayStageName
        DefinitionBody:
          'Fn::Transform':
            Name: 'AWS::Include'
            Parameters:
              Location:
                Fn::Sub:
                - s3://${BucketName}/${SwaggerSpecificationS3Key}
                - BucketName:
                    Fn::ImportValue:
                      !Sub "${EnvironmentName}-dist-bucket-${AWS::Region}" 



ApiGatewayApi:
    Type: AWS::Serverless::Api
    Properties:
        Name: !Sub ${AWS::StackName}-API
        StageName: !Ref ApiGatewayStageName
        DefinitionBody:
          'Fn::Transform':
            Name: 'AWS::Include'
            Parameters:
              Location:
                Fn::Sub:
                - s3://${BucketName}/${SwaggerSpecificationS3Key}
                - BucketName:
                    !ImportValue 'dev-dist-bucket-us-east-1' 



ApiGatewayApi:
    Type: AWS::Serverless::Api
    Properties:
        Name: !Sub ${AWS::StackName}-API
        StageName: !Ref ApiGatewayStageName
        DefinitionBody:
          'Fn::Transform':
            Name: 'AWS::Include'
            Parameters:
              Location:
                Fn::Sub:
                - s3://${BucketName}/${SwaggerSpecificationS3Key}
                - BucketName:
                    Fn::ImportValue: 'dev-dist-bucket-us-east-1'

Cloudformation显示以下错误 .

FAILED - 变换Include下参数Location的值必须解析为字符串，数字，布尔值或其中任何一个的列表 .

但是，如果我不使用 ImportValue 它适用于嵌套的 Fn::Sub

ApiGatewayApi:
    Type: AWS::Serverless::Api
    Properties:
        Name: !Sub ${AWS::StackName}-API
        StageName: !Ref ApiGatewayStageName
        DefinitionBody:
          'Fn::Transform':
            Name: 'AWS::Include'
            Parameters:
              Location:
                Fn::Sub:
                - s3://${BucketName}/${SwaggerSpecificationS3Key}
                - BucketName:
                    Fn::Sub: dist-bucket-${EnvironmentName}-${AWS::Region}

是因为Fn :: Transform还是AWS :: Include？