Added nil guard to blue green settings in google_container_node_pool (#7996) (#5671)

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/7996.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+container: fixed a crash when all zero values are specified `google_container_node_pool.upgrade_settings.blue_green_settings.standard_rollout_policy` subfields
+```

google-beta/resource_container_node_pool.go

@@ -1658,13 +1658,14 @@ func nodePoolUpdate(d *schema.ResourceData, meta interface{}, nodePoolInfo *Node
 
 				if v, ok := blueGreenSettingsConfig["standard_rollout_policy"]; ok && len(v.([]interface{})) > 0 {
 					standardRolloutPolicy := &container.StandardRolloutPolicy{}
-					standardRolloutPolicyConfig := v.([]interface{})[0].(map[string]interface{})
-					standardRolloutPolicy.BatchSoakDuration = standardRolloutPolicyConfig["batch_soak_duration"].(string)
-					if v, ok := standardRolloutPolicyConfig["batch_node_count"]; ok {
-						standardRolloutPolicy.BatchNodeCount = int64(v.(int))
-					}
-					if v, ok := standardRolloutPolicyConfig["batch_percentage"]; ok {
-						standardRolloutPolicy.BatchPercentage = v.(float64)
+					if standardRolloutPolicyConfig, ok := v.([]interface{})[0].(map[string]interface{}); ok {
+						standardRolloutPolicy.BatchSoakDuration = standardRolloutPolicyConfig["batch_soak_duration"].(string)
+						if v, ok := standardRolloutPolicyConfig["batch_node_count"]; ok {
+							standardRolloutPolicy.BatchNodeCount = int64(v.(int))
+						}
+						if v, ok := standardRolloutPolicyConfig["batch_percentage"]; ok {
+							standardRolloutPolicy.BatchPercentage = v.(float64)
+						}
 					}
 					blueGreenSettings.StandardRolloutPolicy = standardRolloutPolicy
 				}