Add forced casting for Arrays in Remove-NullProperties (#50)

This adds a forced cast inside the method that prevents Powershell from
converting a single valued array to an object.

This pr does not include changes to the test methods as Im not sure how
the team would intend the use case to be tested

Its a revisit on #35

Signed-off-by: Laura Rodriguez <rdz.maria.laura@gmail.com>

src/Okta.PowerShell/Client/JsonHelper.ps1

@@ -1,10 +1,10 @@
-#
-# Okta Management
-# Allows customers to easily access the Okta Management APIs
-# Version: 3.0.0
-# Contact: devex-public@okta.com
-# Generated by OpenAPI Generator: https://openapi-generator.tech
-#
+#
+# Okta Management
+# Allows customers to easily access the Okta Management APIs
+# Version: 3.0.0
+# Contact: devex-public@okta.com
+# Generated by OpenAPI Generator: https://openapi-generator.tech
+#
 
 
 # Remove null properties from an object recursively
@@ -33,7 +33,12 @@ function Remove-NullProperties {
         $PropertyList = $InputObject.PSObject.Properties | Where-Object { $null -ne $_.Value }
 
         foreach ($Property in $PropertyList) { 
-            $NewObject[$Property.Name] = Remove-NullProperties $Property.Value
+            if($Property.Value -is [array]){
+                # explicit cast to avoid arrays to be converted to object (i.e @('foo'))
+                $NewObject[$Property.Name] = [array]@(Remove-NullProperties $Property.Value)
+            }else{
+                $NewObject[$Property.Name] = Remove-NullProperties $Property.Value
+            }
         }
     }