[Powershell] Bug with "New-<ClassName>" cmdlets in Model folder.

Description

We have used the Swagger Codegen to generate the Powershell SDK and C# SDK, C# SDK is placed inside the Powershell SDK and the generated powershell cmdlets internally invokes the C# methods.

We have observed few issues with the generated cmdlets

1. When "New-<ClassName>" cmdlets are used we get errors, while digging deeper we have observed that there is a mismatch between the number of arguments in the constructor of the class (<ClassName>) defined in C# SDK and the number of arguments with which the Powershell SDK is trying to call the same constructor inside "New-<ClassName>" cmdlets.

2. In "New-<ClassName>" cmdlets in Model folder, some of the parameter types are defined as "System.Nullable", so when we run the cmdlet getting the error message as "'System.Nullable`1[T]' violates the constraint of type 'T'". If we remove the "System.Nullable" then we are able to proceed.

3. Powershell by default converts all Null into [String]::Empty for String Parameters, So when a object is returned by running the Cmdlets, then the string parameters are set to [String]::Empty instead of NULL value. So we had to manually add the following code in the cmdlet file to overcome the problem for all the string parameters.

if($Moid -eq [String]::Empty)
{
$Moid = [NullString]::Value
}

SDK Link:
https://cdn.intersight.com/components/an-apidocs/1.0.5-99/model/IntersightPowerShellSDK.tar.gz

Swagger-codegen version

Version: 2.2.3

Swagger declaration file content or url

https://cdn.intersight.com/components/an-apidocs/1.0.5-99/model/restapi.json

Command line used for generation

Powershell SDK Generation
java -jar /usr/local/bin/swagger-codegen-cli.jar generate -i ../doc/rest/api/restapi-v2.yaml -DapiTests=false,apiDocs=false,modelTests=false,modelDocs=false -c codegen/config_powershell.json -l powershell -o ../sdk/PowerShellSDK

C# SDK Generation
java -jar /usr/local/bin/swagger-codegen-cli.jar generate -i ../doc/rest/api/restapi-v2.yaml -DapiTests=false,apiDocs=false,modelTests=false,modelDocs=false -c codegen/config_powershell.json -l csharp -o ../sdk/PowerShellSDK/csharp/swaggerClient/

Content of config_powershell.json file

{
"packageName" : "intersight",
"packageVersion" : "1.0.0"
}

Steps to reproduce

1. Download the SDK from the link given above.
2. Open Powershell Window
3. run "./build.ps1" from the SDK folder.
4. Run "Import-Module .\src\intersight\intersight.psd1"
5. Run "New-ComputeBlade"

Related issues/PRs

None

Suggest a fix/enhancement

None

Start by reviewing config_powershell.json and reproducing the failures with build.ps1, Import-Module .\src\intersight\intersight.psd1, and New-ComputeBlade. Trace the generated New- model cmdlets and their C# constructors; done means the reported argument, nullable-type, and null-string problems are reproducibly resolved.