fix clb nil pointer panic (#1763)

* fix clb nil pointer panic

* add changelog

* fix nil pointer for the related string method of helper.transform

Author: lyu571

.changelog/1763.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+tencentcloud_clb_instance: fix the nil exception caused by the security_groups 
+```

tencentcloud/internal/helper/transform.go

@@ -85,15 +85,19 @@ func PInt64(pointer *int64) int64 {
 func InterfacesStrings(configured []interface{}) []string {
 	vs := make([]string, 0, len(configured))
 	for _, v := range configured {
-		vs = append(vs, v.(string))
+		if v != nil {
+			vs = append(vs, v.(string))
+		}
 	}
 	return vs
 }
 
 func InterfacesStringsPoint(configured []interface{}) []*string {
 	vs := make([]*string, 0, len(configured))
 	for _, v := range configured {
-		vs = append(vs, String(v.(string)))
+		if v != nil {
+			vs = append(vs, String(v.(string)))
+		}
 	}
 	return vs
 }

tencentcloud/resource_tc_clb_instance.go

@@ -506,8 +506,10 @@ func resourceTencentCloudClbInstanceCreate(d *schema.ResourceData, meta interfac
 		securityGroups := v.([]interface{})
 		sgRequest.SecurityGroups = make([]*string, 0, len(securityGroups))
 		for i := range securityGroups {
-			securityGroup := securityGroups[i].(string)
-			sgRequest.SecurityGroups = append(sgRequest.SecurityGroups, &securityGroup)
+			if securityGroups[i] != nil {
+				securityGroup := securityGroups[i].(string)
+				sgRequest.SecurityGroups = append(sgRequest.SecurityGroups, &securityGroup)
+			}
 		}
 		err := resource.Retry(writeRetryTimeout, func() *resource.RetryError {
 			sgResponse, e := meta.(*TencentCloudClient).apiV3Conn.UseClbClient().SetLoadBalancerSecurityGroups(sgRequest)