Update CHANGELOG.md for #39279

CHANGELOG.md

@@ -49,6 +49,7 @@ BUG FIXES:
 * resource/aws_eks_cluster: Return `created_at` as an [RFC3339](https://www.rfc-editor.org/rfc/rfc3339) formatted timestamp ([#24183](https://github.com/hashicorp/terraform-provider-aws/issues/24183))
 * resource/aws_iam_role: Fix to reduce Terraform reporting differences when a role's ARN temporarily appears as the role's unique ID ([#36794](https://github.com/hashicorp/terraform-provider-aws/issues/36794))
 * resource/aws_networkfirewall_tls_inspection_configuration: Fix issue where `check_certificate_revovation_status` is ignored due to bad autoflex field mapping ([#39211](https://github.com/hashicorp/terraform-provider-aws/issues/39211))
+* resource/aws_networkmonitor_monitor: Fixes error when optional attribute `aggregation_period` not set. ([#39279](https://github.com/hashicorp/terraform-provider-aws/issues/39279))
 * resource/aws_quicksight_data_set: Change `permissions.actions` `MaxItems` from `16` to `20`. This fixes a regression introduced in [v5.66.0](https://github.com/hashicorp/terraform-provider-aws/blob/main/CHANGELOG.md#5660-september--5-2024) ([#39226](https://github.com/hashicorp/terraform-provider-aws/issues/39226))
 * resource/aws_quicksight_vpc_connection: Remove `vpc_connection_id` regular expression validator. This fixes a regression introduced in [v5.66.0](https://github.com/hashicorp/terraform-provider-aws/blob/main/CHANGELOG.md#5660-september--5-2024) ([#39231](https://github.com/hashicorp/terraform-provider-aws/issues/39231))
 * resource/aws_sesv2_configuration_set: Allow `suppression_options.suppressed_reasons` to be an empty list (`[]`) in order to disable the suppression list ([#29671](https://github.com/hashicorp/terraform-provider-aws/issues/29671))