fix key_id update exception (#1688)

* fix key_id update exception

* add changelog

---------

Co-authored-by: mikatong <mikatong@tencent.com>

Author: tongyiming

.changelog/1688.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+resource/tencentcloud_instance: fix key_ids update exception
+```

tencentcloud/resource_tc_instance.go

@@ -1341,6 +1341,8 @@ func resourceTencentCloudInstanceUpdate(d *schema.ResourceData, meta interface{}
 
 			adds := nv.Difference(ov)
 			removes := ov.Difference(nv)
+			adds.Remove("")
+			removes.Remove("")
 
 			if removes.Len() > 0 {
 				err := cvmService.UnbindKeyPair(ctx, helper.InterfacesStringsPoint(removes.List()), []*string{&instanceId})

tencentcloud/resource_tc_instance_test.go

@@ -214,6 +214,15 @@ func TestAccTencentCloudInstanceResource_WithKeyPairs(t *testing.T) {
 		Providers:     testAccProviders,
 		CheckDestroy:  testAccCheckInstanceDestroy,
 		Steps: []resource.TestStep{
+			{
+				PreConfig: func() { testAccStepPreConfigSetTempAKSK(t, ACCOUNT_TYPE_COMMON) },
+				Config:    testAccTencentCloudInstanceWithKeyPair_withoutKeyPair,
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckTencentCloudDataSourceID(id),
+					testAccCheckTencentCloudInstanceExists(id),
+					resource.TestCheckResourceAttr(id, "instance_status", "RUNNING"),
+				),
+			},
 			{
 				PreConfig: func() { testAccStepPreConfigSetTempAKSK(t, ACCOUNT_TYPE_COMMON) },
 				Config: testAccTencentCloudInstanceWithKeyPair(
@@ -938,6 +947,16 @@ resource "tencentcloud_instance" "foo" {
 }
 `
 
+const testAccTencentCloudInstanceWithKeyPair_withoutKeyPair = defaultInstanceVariable + `
+resource "tencentcloud_instance" "foo" {
+	instance_name     = var.instance_name
+	availability_zone = var.availability_cvm_zone
+	image_id          = data.tencentcloud_images.default.images.0.image_id
+	instance_type     = data.tencentcloud_instance_types.default.instance_types.0.instance_type
+	system_disk_type  = "CLOUD_PREMIUM"
+}
+`
+
 func testAccTencentCloudInstanceWithKeyPair(keyIds string) string {
 
 	return fmt.Sprintf(