fix: [M3-10709] - firewall_id error on LKE pool update (#13109)

* Fix firewall_id error on LKE E pool update

* Added changeset: The `firewall_id` error on LKE pool update

* Add comments and update false check instances

* Revert accidental removal of update_strategy

Author: pmakode-akamai

packages/manager/.changeset/pr-13109-fixed-1763535418420.md

@@ -0,0 +1,5 @@
+---
+"@linode/manager": Fixed
+---
+
+The `firewall_id` error on LKE pool update ([#13109](https://github.com/linode/manager/pull/13109))

packages/manager/src/features/Kubernetes/KubernetesClusterDetail/NodePoolsDisplay/ConfigureNodePool/ConfigureNodePoolForm.tsx

@@ -46,7 +46,13 @@ export const ConfigureNodePoolForm = (props: Props) => {
       // @TODO allow users to edit Node Pool `label` and `tags` because the API supports it. (ECE-353)
       // label: nodePool.label,
       // tags: nodePool.tags,
-      firewall_id: nodePool.firewall_id,
+
+      /**
+       * We set the default value of the form field to `undefined` if `nodePool.firewall_id` is null.
+       * This ensures the field remains controlled in React Hook Form and is properly initialized,
+       * preventing unexpected validation errors when the initial value is null.
+       */
+      firewall_id: nodePool.firewall_id ?? undefined,
       update_strategy: nodePool.update_strategy,
       k8s_version: nodePool.k8s_version,
     },
@@ -87,7 +93,7 @@ export const ConfigureNodePoolForm = (props: Props) => {
             clusterTier={clusterTier ?? 'standard'}
             firewallSelectOptions={{
               allowFirewallRemoval: clusterTier === 'standard',
-              ...(nodePool.firewall_id !== 0 && {
+              ...(nodePool.firewall_id !== null && {
                 disableDefaultFirewallRadio: true,
                 defaultFirewallRadioTooltip:
                   "You can't use this option once an existing Firewall has been selected.",