diff --git a/terraform/slurm_cluster/examples/slurm_cluster/test_cluster/README_TF.md b/terraform/slurm_cluster/examples/slurm_cluster/test_cluster/README_TF.md
index 1d603b1f..17d42ae5 100644
--- a/terraform/slurm_cluster/examples/slurm_cluster/test_cluster/README_TF.md
+++ b/terraform/slurm_cluster/examples/slurm_cluster/test_cluster/README_TF.md
@@ -87,7 +87,7 @@ No resources.
 | <a name="input_source_image_project"></a> [source\_image\_project](#input\_source\_image\_project) | Project where the source image comes from. If it is not provided, the provider project is used. | `string` | `""` | no |
 | <a name="input_subnets"></a> [subnets](#input\_subnets) | The list of subnets being created. | `list(map(string))` | `[]` | no |
 | <a name="input_subnetwork"></a> [subnetwork](#input\_subnetwork) | Default subnet to deploy to. | `string` | `"default"` | no |
-| <a name="input_subnetwork_project"></a> [subnetwork\_project](#input\_subnetwork\_project) | The project that subnetwork belongs to | `string` | `""` | no |
+| <a name="input_subnetwork_project"></a> [subnetwork\_project](#input\_subnetwork\_project) | The project that subnetwork belongs to | `string` | `null` | no |
 
 ## Outputs
 
diff --git a/terraform/slurm_cluster/examples/slurm_cluster/test_cluster/variables.tf b/terraform/slurm_cluster/examples/slurm_cluster/test_cluster/variables.tf
index af634911..f9164121 100644
--- a/terraform/slurm_cluster/examples/slurm_cluster/test_cluster/variables.tf
+++ b/terraform/slurm_cluster/examples/slurm_cluster/test_cluster/variables.tf
@@ -56,7 +56,7 @@ variable "subnetwork" {
 variable "subnetwork_project" {
   description = "The project that subnetwork belongs to"
   type        = string
-  default     = ""
+  default     = null
 }
 
 ###########
diff --git a/terraform/slurm_cluster/modules/_instance_template/README_TF.md b/terraform/slurm_cluster/modules/_instance_template/README_TF.md
index 5e7fe2c0..8c90591a 100644
--- a/terraform/slurm_cluster/modules/_instance_template/README_TF.md
+++ b/terraform/slurm_cluster/modules/_instance_template/README_TF.md
@@ -89,7 +89,7 @@ No modules.
 | <a name="input_stack_type"></a> [stack\_type](#input\_stack\_type) | The stack type for this network interface to identify whether the IPv6 feature is enabled or not. Values are `IPV4_IPV6` or `IPV4_ONLY`. Default behavior is equivalent to IPV4\_ONLY. | `string` | `null` | no |
 | <a name="input_startup_script"></a> [startup\_script](#input\_startup\_script) | User startup script to run when instances spin up | `string` | `""` | no |
 | <a name="input_subnetwork"></a> [subnetwork](#input\_subnetwork) | The name of the subnetwork to attach this interface to. The subnetwork must exist in the same region this instance will be created in. Either network or subnetwork must be provided. | `string` | `""` | no |
-| <a name="input_subnetwork_project"></a> [subnetwork\_project](#input\_subnetwork\_project) | The ID of the project in which the subnetwork belongs. If it is not provided, the provider project is used. | `string` | `""` | no |
+| <a name="input_subnetwork_project"></a> [subnetwork\_project](#input\_subnetwork\_project) | The ID of the project in which the subnetwork belongs. If it is not provided, the provider project is used. | `string` | `null` | no |
 | <a name="input_tags"></a> [tags](#input\_tags) | Network tags, provided as a list | `list(string)` | `[]` | no |
 | <a name="input_threads_per_core"></a> [threads\_per\_core](#input\_threads\_per\_core) | The number of threads per physical core. To disable simultaneous multithreading (SMT) set this to 1. | `number` | `null` | no |
 | <a name="input_total_egress_bandwidth_tier"></a> [total\_egress\_bandwidth\_tier](#input\_total\_egress\_bandwidth\_tier) | Network bandwidth tier. Note: machine\_type must be a supported type. Values are 'TIER\_1' or 'DEFAULT'.<br/>See https://cloud.google.com/compute/docs/networking/configure-vm-with-high-bandwidth-configuration for details. | `string` | `"DEFAULT"` | no |
diff --git a/terraform/slurm_cluster/modules/_instance_template/variables.tf b/terraform/slurm_cluster/modules/_instance_template/variables.tf
index d04b0161..128305f7 100644
--- a/terraform/slurm_cluster/modules/_instance_template/variables.tf
+++ b/terraform/slurm_cluster/modules/_instance_template/variables.tf
@@ -200,7 +200,7 @@ variable "subnetwork" {
 variable "subnetwork_project" {
   description = "The ID of the project in which the subnetwork belongs. If it is not provided, the provider project is used."
   type        = string
-  default     = ""
+  default     = null
 }
 
 variable "network_ip" {
diff --git a/terraform/slurm_cluster/modules/_slurm_instance/README_TF.md b/terraform/slurm_cluster/modules/_slurm_instance/README_TF.md
index ae47061e..febf151c 100644
--- a/terraform/slurm_cluster/modules/_slurm_instance/README_TF.md
+++ b/terraform/slurm_cluster/modules/_slurm_instance/README_TF.md
@@ -68,7 +68,7 @@ No modules.
 | <a name="input_slurm_instance_role"></a> [slurm\_instance\_role](#input\_slurm\_instance\_role) | Slurm instance type. Must be one of: controller; login; compute. | `string` | `null` | no |
 | <a name="input_static_ips"></a> [static\_ips](#input\_static\_ips) | List of static IPs for VM instances | `list(string)` | `[]` | no |
 | <a name="input_subnetwork"></a> [subnetwork](#input\_subnetwork) | Subnet to deploy to. Only one of network or subnetwork should be specified. | `string` | `""` | no |
-| <a name="input_subnetwork_project"></a> [subnetwork\_project](#input\_subnetwork\_project) | The project that subnetwork belongs to | `string` | `""` | no |
+| <a name="input_subnetwork_project"></a> [subnetwork\_project](#input\_subnetwork\_project) | The project that subnetwork belongs to | `string` | `null` | no |
 | <a name="input_zone"></a> [zone](#input\_zone) | Zone where the instances should be created. If not specified, instances will be spread across available zones in the region. | `string` | `null` | no |
 
 ## Outputs
diff --git a/terraform/slurm_cluster/modules/_slurm_instance/variables.tf b/terraform/slurm_cluster/modules/_slurm_instance/variables.tf
index 3adb24f1..697d5c4b 100644
--- a/terraform/slurm_cluster/modules/_slurm_instance/variables.tf
+++ b/terraform/slurm_cluster/modules/_slurm_instance/variables.tf
@@ -36,7 +36,7 @@ variable "subnetwork" {
 variable "subnetwork_project" {
   description = "The project that subnetwork belongs to"
   type        = string
-  default     = ""
+  default     = null
 }
 
 variable "hostname" {
diff --git a/terraform/slurm_cluster/modules/slurm_controller_instance/README_TF.md b/terraform/slurm_cluster/modules/slurm_controller_instance/README_TF.md
index 7c064151..614fb88b 100644
--- a/terraform/slurm_cluster/modules/slurm_controller_instance/README_TF.md
+++ b/terraform/slurm_cluster/modules/slurm_controller_instance/README_TF.md
@@ -63,7 +63,7 @@ limitations under the License.
 | <a name="input_slurm_cluster_name"></a> [slurm\_cluster\_name](#input\_slurm\_cluster\_name) | The cluster name, used for resource naming and slurm accounting. | `string` | n/a | yes |
 | <a name="input_static_ips"></a> [static\_ips](#input\_static\_ips) | List of static IPs for VM instances. | `list(string)` | `[]` | no |
 | <a name="input_subnetwork"></a> [subnetwork](#input\_subnetwork) | Subnet to deploy to. Only one of network or subnetwork should be specified. | `string` | `""` | no |
-| <a name="input_subnetwork_project"></a> [subnetwork\_project](#input\_subnetwork\_project) | The project that subnetwork belongs to. | `string` | `""` | no |
+| <a name="input_subnetwork_project"></a> [subnetwork\_project](#input\_subnetwork\_project) | The project that subnetwork belongs to. | `string` | `null` | no |
 | <a name="input_zone"></a> [zone](#input\_zone) | Zone where the instances should be created. If not specified, instances will be<br/>spread across available zones in the region. | `string` | `null` | no |
 
 ## Outputs
diff --git a/terraform/slurm_cluster/modules/slurm_controller_instance/variables.tf b/terraform/slurm_cluster/modules/slurm_controller_instance/variables.tf
index 61a3cf6f..f07839d3 100644
--- a/terraform/slurm_cluster/modules/slurm_controller_instance/variables.tf
+++ b/terraform/slurm_cluster/modules/slurm_controller_instance/variables.tf
@@ -38,7 +38,7 @@ variable "subnetwork" {
 variable "subnetwork_project" {
   type        = string
   description = "The project that subnetwork belongs to."
-  default     = ""
+  default     = null
 }
 
 variable "region" {
diff --git a/terraform/slurm_cluster/modules/slurm_login_instance/README_TF.md b/terraform/slurm_cluster/modules/slurm_login_instance/README_TF.md
index 7b7c1084..82e12469 100644
--- a/terraform/slurm_cluster/modules/slurm_login_instance/README_TF.md
+++ b/terraform/slurm_cluster/modules/slurm_login_instance/README_TF.md
@@ -51,7 +51,7 @@ No resources.
 | <a name="input_slurm_cluster_name"></a> [slurm\_cluster\_name](#input\_slurm\_cluster\_name) | Cluster name, used for resource naming. | `string` | n/a | yes |
 | <a name="input_static_ips"></a> [static\_ips](#input\_static\_ips) | List of static IPs for VM instances. | `list(string)` | `[]` | no |
 | <a name="input_subnetwork"></a> [subnetwork](#input\_subnetwork) | Subnet to deploy to. Only one of network or subnetwork should be specified. | `string` | `""` | no |
-| <a name="input_subnetwork_project"></a> [subnetwork\_project](#input\_subnetwork\_project) | The project that subnetwork belongs to. | `string` | `""` | no |
+| <a name="input_subnetwork_project"></a> [subnetwork\_project](#input\_subnetwork\_project) | The project that subnetwork belongs to. | `string` | `null` | no |
 | <a name="input_suffix"></a> [suffix](#input\_suffix) | Login name suffix. | `string` | `"frontend"` | no |
 | <a name="input_zone"></a> [zone](#input\_zone) | Zone where the instances should be created. If not specified, instances will be<br/>spread across available zones in the region. | `string` | `null` | no |
 
diff --git a/terraform/slurm_cluster/modules/slurm_login_instance/variables.tf b/terraform/slurm_cluster/modules/slurm_login_instance/variables.tf
index 4464110b..a3704ca7 100644
--- a/terraform/slurm_cluster/modules/slurm_login_instance/variables.tf
+++ b/terraform/slurm_cluster/modules/slurm_login_instance/variables.tf
@@ -65,7 +65,7 @@ variable "subnetwork" {
 variable "subnetwork_project" {
   type        = string
   description = "The project that subnetwork belongs to."
-  default     = ""
+  default     = null
 }
 
 variable "region" {