fix: set the default value as null and fixed validation

Author: imprateeksh

README.md

@@ -198,7 +198,7 @@ To attach access management tags to resources in this module, you need the follo
 | <a name="input_dns_records"></a> [dns\_records](#input\_dns\_records) | List of DNS records to be created. | <pre>list(object({<br/>    name       = string<br/>    type       = string<br/>    ttl        = number<br/>    rdata      = string<br/>    preference = optional(number, null)<br/>    service    = optional(string, null)<br/>    protocol   = optional(string, null)<br/>    priority   = optional(number, null)<br/>    weight     = optional(number, null)<br/>    port       = optional(number, null)<br/>  }))</pre> | `[]` | no |
 | <a name="input_dns_zone_description"></a> [dns\_zone\_description](#input\_dns\_zone\_description) | The description of the DNS zone. | `string` | `"Default DNS Zone"` | no |
 | <a name="input_dns_zone_label"></a> [dns\_zone\_label](#input\_dns\_zone\_label) | Label associated with the DNS zone. | `string` | `"dns-zone"` | no |
-| <a name="input_dns_zone_name"></a> [dns\_zone\_name](#input\_dns\_zone\_name) | The name of the DNS zone to be created. | `string` | `"slz.com"` | no |
+| <a name="input_dns_zone_name"></a> [dns\_zone\_name](#input\_dns\_zone\_name) | The name of the DNS zone to be created. | `string` | `null` | no |
 | <a name="input_enable_hub"></a> [enable\_hub](#input\_enable\_hub) | Indicates whether this VPC is enabled as a DNS name resolution hub. | `bool` | `false` | no |
 | <a name="input_enable_hub_vpc_crn"></a> [enable\_hub\_vpc\_crn](#input\_enable\_hub\_vpc\_crn) | Indicates whether Hub VPC CRN is passed. | `bool` | `false` | no |
 | <a name="input_enable_hub_vpc_id"></a> [enable\_hub\_vpc\_id](#input\_enable\_hub\_vpc\_id) | Indicates whether Hub VPC ID is passed. | `bool` | `false` | no |

variables.tf

@@ -640,10 +640,10 @@ variable "dns_plan" {
 
 variable "dns_zone_name" {
   description = "The name of the DNS zone to be created."
-  default     = "slz.com"
+  default     = null
   type        = string
   validation {
-    condition = var.dns_zone_name == null || !contains([
+    condition = var.dns_zone_name == null ? true : !contains([
       "ibm.com",
       "softlayer.com",
       "bluemix.net",