diff --git a/modules/openapi-generator/src/main/resources/powershell/api_client.mustache b/modules/openapi-generator/src/main/resources/powershell/api_client.mustache
index 2e6cb8647ce..69cac6ca809 100644
--- a/modules/openapi-generator/src/main/resources/powershell/api_client.mustache
+++ b/modules/openapi-generator/src/main/resources/powershell/api_client.mustache
@@ -235,6 +235,7 @@ function DeserializeResponse {
         [Parameter(Mandatory)]
         [Object]$Response,
         [Parameter(Mandatory)]
+        [AllowNull()]
         [AllowEmptyCollection()]
         [string[]]$ContentTypes
     )
diff --git a/samples/client/echo_api/powershell/src/PSOpenAPITools/Private/ApiClient.ps1 b/samples/client/echo_api/powershell/src/PSOpenAPITools/Private/ApiClient.ps1
index 08c35f11b33..95094512d35 100644
--- a/samples/client/echo_api/powershell/src/PSOpenAPITools/Private/ApiClient.ps1
+++ b/samples/client/echo_api/powershell/src/PSOpenAPITools/Private/ApiClient.ps1
@@ -223,6 +223,7 @@ function DeserializeResponse {
         [Parameter(Mandatory)]
         [Object]$Response,
         [Parameter(Mandatory)]
+        [AllowNull()]
         [AllowEmptyCollection()]
         [string[]]$ContentTypes
     )
diff --git a/samples/client/petstore/powershell/src/PSPetstore/Private/PSApiClient.ps1 b/samples/client/petstore/powershell/src/PSPetstore/Private/PSApiClient.ps1
index 4bd3084c7e4..1dc3939d315 100755
--- a/samples/client/petstore/powershell/src/PSPetstore/Private/PSApiClient.ps1
+++ b/samples/client/petstore/powershell/src/PSPetstore/Private/PSApiClient.ps1
@@ -239,6 +239,7 @@ function DeserializeResponse {
         [Parameter(Mandatory)]
         [Object]$Response,
         [Parameter(Mandatory)]
+        [AllowNull()]
         [AllowEmptyCollection()]
         [string[]]$ContentTypes
     )