title: Cloudformation template Lambda environment variable error - Value of property Variables must be an object with String
body: <p>I want to set environment variiable for my lambda function using cloudformation mappings. Hence I am using <code>Fn::FindInMap</code> to get the value of variable from a mapping. But I am getting the error - <code>Value of property Variables must be an object with String (or simple type) properties</code></p>
  
  <pre><code>Mappings:
    DomainResourceMapping:
      DUBCrossAccountIAMRole:
        beta: "xyz"
        prod: "act"
  
  Resources:
    LambdaFunction:
      Type: AWS::Serverless::Function
      Properties:
        Handler: '...t'
        Runtime: java8
        CodeUri:
          Bucket: ...
          Key: ...
        Description: nn
        Timeout: 20
        MemorySize: 512
        Environment:
          Variables:
            DUB_CROSS_ACCOUNT_IAM_ROLE:
            - Fn::FindInMap:
              - DomainResourceMapping
              - DUBCrossAccountIAMRole
              - {Ref: Stage}
  </code></pre>