Setting Dynamic Variable value to empty "" not working

Hi Octopus team,

I have a dynamic variable BuildNumber, and set it to empty string like this Set-OctopusVariable -name “BuildNumber” -value ""
When I do a deployment,
This statement “#{Octopus.Action[Retrieve Build Number].Output.BuildNumber}” should return empty string ""
but instead, it returns “#{Octopus.Action[Retrieve Build Number].Output.BuildNumber}”

I am guessing this is the designed behavior for Octopus, if so, how can I accomplish my results that I want?

Thanks in advance.