unable to update authenticator_groups_config (#6755) (#4918)

* unable to update authenticator_groups_config

Co-authored-by: Edward Sun <[email protected]>
Signed-off-by: Modular Magician <[email protected]>

Signed-off-by: Modular Magician <[email protected]>
Co-authored-by: Edward Sun <[email protected]>

Author: modular-magician

.changelog/6755.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+container: fixed unable to update `authenticator_groups_config` on `google_container_cluster`
+```

google-beta/resource_container_cluster.go

@@ -4274,9 +4274,16 @@ func expandContainerClusterAuthenticatorGroupsConfig(configured interface{}) *co
 	}
 
 	config := l[0].(map[string]interface{})
-	return &container.AuthenticatorGroupsConfig{
-		SecurityGroup: config["security_group"].(string),
+	result := &container.AuthenticatorGroupsConfig{}
+	if securityGroup, ok := config["security_group"]; ok {
+		if securityGroup == nil || securityGroup.(string) == "" {
+			result.Enabled = false
+		} else {
+			result.Enabled = true
+			result.SecurityGroup = securityGroup.(string)
+		}
 	}
+	return result
 }
 
 func expandNodePoolDefaults(configured interface{}) *container.NodePoolDefaults {