d/aws_ec2_transit_gateway: fix crash setting encryption_support

Author: YakDriver

.changelog/45462.txt

@@ -1,3 +1,7 @@
 ```release-note:bug
 resource/aws_ec2_transit_gateway: Fix potential crash when setting `encryption_support`. This addresses a regression introduced in [v6.25.0](https://github.com/hashicorp/terraform-provider-aws/blob/main/CHANGELOG.md#6250-december-4-2025).
 ```
+
+```release-note:bug
+data-source/aws_ec2_transit_gateway: Fix potential crash when reading `encryption_support`. This addresses a regression introduced in [v6.25.0](https://github.com/hashicorp/terraform-provider-aws/blob/main/CHANGELOG.md#6250-december-4-2025).
+```

internal/service/ec2/transitgateway_data_source.go

@@ -137,14 +137,18 @@ func dataSourceTransitGatewayRead(ctx context.Context, d *schema.ResourceData, m
 	d.Set("default_route_table_propagation", transitGateway.Options.DefaultRouteTablePropagation)
 	d.Set(names.AttrDescription, transitGateway.Description)
 	d.Set("dns_support", transitGateway.Options.DnsSupport)
-	var encryptionSupport string
-	encryptionState := transitGateway.Options.EncryptionSupport.EncryptionState
-	if encryptionState == awstypes.EncryptionStateValueEnabled || encryptionState == awstypes.EncryptionStateValueEnabling {
-		encryptionSupport = string(awstypes.EncryptionSupportOptionValueEnable)
-	} else {
-		encryptionSupport = string(awstypes.EncryptionSupportOptionValueDisable)
+
+	if transitGateway.Options.EncryptionSupport != nil {
+		var encryptionSupport string
+		encryptionState := transitGateway.Options.EncryptionSupport.EncryptionState
+		if encryptionState == awstypes.EncryptionStateValueEnabled || encryptionState == awstypes.EncryptionStateValueEnabling {
+			encryptionSupport = string(awstypes.EncryptionSupportOptionValueEnable)
+		} else {
+			encryptionSupport = string(awstypes.EncryptionSupportOptionValueDisable)
+		}
+		d.Set("encryption_support", encryptionSupport)
 	}
-	d.Set("encryption_support", encryptionSupport)
+
 	d.Set("multicast_support", transitGateway.Options.MulticastSupport)
 	d.Set(names.AttrOwnerID, transitGateway.OwnerId)
 	d.Set("propagation_default_route_table_id", transitGateway.Options.PropagationDefaultRouteTableId)