title: Aws cli cloudformation error seen on passing parameter value of type CommaDelimitedList
body: <p>I am seeing an invalid-type error for a CommaDelimitedList parameter value. The CF runs without any errors from the console.</p>
  
  <p>AWS CLI command: </p>
  
  <pre><code>aws cloudformation create-stack --stack-name agkTestUserStack --template-body file://api_user.yaml --parameters ParameterKey=CustomUserName,ParameterValue="svc_TestUser" ParameterKey=GroupAssociations,ParameterValue="Dev,Test"
  </code></pre>
  
  <p>Output: </p>
  
  <pre><code>Parameter validation failed:
  Invalid type for parameter Parameters[1].ParameterValue, value: [u'Dev', u'Test'], type: &lt;type 'list'&gt;, valid types: &lt;type 'basestring'&gt;
  </code></pre>
  
  <p>AWS CLI version: aws-cli/1.15.75 Python/2.7.9 Windows/8 botocore/1.10.74</p>
  
  <p>api_user.yaml:</p>
  
  <pre><code>AWSTemplateFormatVersion: 2010-09-09
  Parameters:
    CustomUserName:
      Type: String
      Description: Custom user name
      Default: ''
    GroupAssociations:
      Type: CommaDelimitedList
      Description: Comma-delimited list of groups to associate the user
      Default: ''
  Conditions:
    NoGroups: !Equals 
      - !Join
          - ''
          - !Ref GroupAssociations
      - '' 
    NoUserName: !Equals 
      - !Ref CustomUserName 
      - ''
  Resources:
    CustomUser:
      Type: 'AWS::IAM::User'
      Properties:
        UserName: !If
          - NoUserName
          - !Ref AWS::NoValue
          - !Ref CustomUserName
        Groups: !If
          - NoGroups 
          - !Ref AWS::NoValue
          - !Ref GroupAssociations 
  Outputs:
    UserName:
      Description: User instance name
      Value: !Ref CustomUser
      Export:
        Name: UserName
    UserArn:
      Description: User instance ARN
      Value: !GetAtt CustomUser.Arn
      Export:
        Name: UserArn
  </code></pre>