AWS::EC2::AvailabilityZone::Name parameter validation...

Question

I have an AWS::EC2::AvailabilityZone::Name as a parameter for my CloudFormation template like this:  
  
  AvailabilityZone:  
    Type: AWS::EC2::AvailabilityZone::Name  
    Description: New subnets will be created for this zone.  
    ConstraintDescription: "A valid availability zone must be selected."  
  
It populates nicely with the list of Availability Zones for the region where the CloudFormation template is coming up. However, CloudFormation does not validate that an Availability Zone was selected (i.e. it can be left blank). After the "Create Stack" button is pushed the stack creation process will fail.  
  
I would like to be able to validate the parameter and make sure that it is not empty before the stack fails. I tried specifying a "MinLength" property of 9. I uploaded the template and it would not let me enter an empty Availability Zone (i.e. it seemed to work). However, in our build process we call cfn-lint to validate the template and it gives the following error:  
  
E2001 Parameter AvailabilityZone has property MinLength which is only valid for $$'String'$$  
  
Can anyone tell me what is the correct way to validate an AWS::EC2::AvailabilityZone::Name field to be non empty at least, and preferably an item in the list provided by the GUI?  
  
Thanks in advance,

hdsiii · Answer

AWS tech support sent me an answer. Although MinLength is not supported on AvailabilityZone::Name, AllowedPattern is. Here is a pattern that ensures the AvailabilityZone::Name is at least 1 character long. Since this is a popup field it ensures that the popup is populated and not left blank.  
  
===================================================  
AvailabilityZone:  
    Type: AWS::EC2::AvailabilityZone::Name  
    Description: EC2 AvailabilityZone  
    AllowedPattern: ".+"                # -> to have a non blank value  
===================================================  
  
FYI: Using a DefaultValue is not really an option since I don't know what Region the script is being run in.

AWS::EC2::AvailabilityZone::Name parameter validation...

=================================================== AvailabilityZone: Type: AWS::EC2::AvailabilityZone::Name Description: EC2 AvailabilityZone AllowedPattern: ".+" # -> to have a non blank value

Relevant content

===================================================
AvailabilityZone:
Type: AWS::EC2::AvailabilityZone::Name
Description: EC2 AvailabilityZone
AllowedPattern: ".+" # -> to have a non blank value