fix failing remove

.changelog/5156.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+Container: fixed a bug in failing to remove `maintenance_exclusion` on `google_container_cluster`
+```

google/resource_container_cluster.go

@@ -2622,7 +2622,7 @@ func expandMaintenancePolicy(d *schema.ResourceData, meta interface{}) *containe
 	}
 	maintenancePolicy := l[0].(map[string]interface{})
 
-	if maintenanceExclusions, ok := maintenancePolicy["maintenance_exclusion"]; ok && len(maintenanceExclusions.(*schema.Set).List()) > 0 {
+	if maintenanceExclusions, ok := maintenancePolicy["maintenance_exclusion"]; ok {
 		for k := range exclusions {
 			delete(exclusions, k)
 		}

google/resource_container_cluster_test.go

@@ -1129,6 +1129,47 @@ func TestAccContainerCluster_withMaintenanceExclusionWindow(t *testing.T) {
 	})
 }
 
+func TestAccContainerCluster_deleteExclusionWindow(t *testing.T) {
+	t.Parallel()
+	cluster := fmt.Sprintf("tf-test-cluster-%s", randString(t, 10))
+	resourceName := "google_container_cluster.with_maintenance_exclusion_window"
+
+	vcrTest(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckContainerClusterDestroyProducer(t),
+		Steps: []resource.TestStep{
+			{
+				Config: testAccContainerCluster_withExclusion_DailyMaintenanceWindow(cluster, "2020-01-01T00:00:00Z", "2020-01-02T00:00:00Z"),
+			},
+			{
+				ResourceName:        resourceName,
+				ImportStateIdPrefix: "us-central1-a/",
+				ImportState:         true,
+				ImportStateVerify:   true,
+			},
+			{
+				Config: testAccContainerCluster_withExclusion_RecurringMaintenanceWindow(cluster, "2019-01-01T00:00:00Z", "2019-01-02T00:00:00Z", "2019-05-01T00:00:00Z", "2019-05-02T00:00:00Z"),
+			},
+			{
+				ResourceName:        resourceName,
+				ImportStateIdPrefix: "us-central1-a/",
+				ImportState:         true,
+				ImportStateVerify:   true,
+			},
+			{
+				Config: testAccContainerCluster_withExclusion_NoMaintenanceWindow(cluster, "2020-01-01T00:00:00Z", "2020-01-02T00:00:00Z"),
+			},
+			{
+				ResourceName:        resourceName,
+				ImportStateIdPrefix: "us-central1-a/",
+				ImportState:         true,
+				ImportStateVerify:   true,
+			},
+		},
+	})
+}
+
 func TestAccContainerCluster_withIPAllocationPolicy_existingSecondaryRanges(t *testing.T) {
 	t.Parallel()
 
@@ -2844,6 +2885,25 @@ resource "google_container_cluster" "with_maintenance_exclusion_window" {
 `, clusterName, w1startTime, w1endTime, w1startTime, w1endTime, w2startTime, w2endTime)
 }
 
+func testAccContainerCluster_withExclusion_NoMaintenanceWindow(clusterName string, w1startTime, w1endTime string) string {
+
+	return fmt.Sprintf(`
+resource "google_container_cluster" "with_maintenance_exclusion_window" {
+  name               = "%s"
+  location           = "us-central1-a"
+  initial_node_count = 1
+
+  maintenance_policy {
+	recurring_window {
+		start_time = "%s"
+		end_time = "%s"
+		recurrence = "FREQ=DAILY"
+	}
+ }
+}
+`, clusterName, w1startTime, w1endTime)
+}
+
 func testAccContainerCluster_withExclusion_DailyMaintenanceWindow(clusterName string, w1startTime, w1endTime string) string {
 
 	return fmt.Sprintf(`