使用import和sub psudo函数返回错误

  usagePlan:
Type: AWS::ApiGateway::UsagePlan
Properties:
  ApiStages:
  - ApiId: !ImportValue: "test-restApi-lambda-send-email-contactus-post"
    Stage: "stg1"
  Description: Customer ABC's usage plan
  Quota:
    Limit: 5000
    Period: MONTH
  Throttle:
    BurstLimit: 200
    RateLimit: 100
  UsagePlanName: Plan_ABC

一切正常,代码正常工作。

  usagePlan:
Type: AWS::ApiGateway::UsagePlan
Properties:
  ApiStages:
  - ApiId:
    Fn::ImportValue: !Sub "${project}-restApi-lambda-send-email-contactus-post"
    Stage: "stg1"
  Description: Customer ABC's usage plan
  Quota:
    Limit: 5000
    Period: MONTH
  Throttle:
    BurstLimit: 200
    RateLimit: 100
  UsagePlanName: Plan_ABC

我得到以下错误:

An error occurred (ValidationError) when calling the CreateStack operation: [/Resources/usagePlan/Type/ApiStages/0/ApiId] 'null' values are not allowed in templates

Fn::ImportValue: !Sub "${project}-restApi-lambda-send-email-contactus-post"