Explicitly set labels to nil for Alert Policy

products/monitoring/terraform.yaml

@@ -27,6 +27,7 @@ overrides: !ruby/object:Overrides::ResourceOverrides
           alert_policy_display_name: "My Alert Policy"
     custom_code: !ruby/object:Provider::Terraform::CustomCode
       custom_import: templates/terraform/custom_import/self_link_as_name.erb
+      decoder: 'templates/terraform/decoders/alert_policy_removed_fields.go.erb'
       post_create: templates/terraform/post_create/set_computed_name.erb
       extra_schema_entry: templates/terraform/extra_schema_entry/alert_policy.erb
 

templates/terraform/decoders/alert_policy_removed_fields.go.erb

@@ -0,0 +1,18 @@
+<%# The license inside this block applies to this file.
+	# Copyright 2019 Google Inc.
+	# Licensed under the Apache License, Version 2.0 (the "License");
+	# you may not use this file except in compliance with the License.
+	# You may obtain a copy of the License at
+	#
+	#     http://www.apache.org/licenses/LICENSE-2.0
+	#
+	# Unless required by applicable law or agreed to in writing, software
+	# distributed under the License is distributed on an "AS IS" BASIS,
+	# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+	# See the License for the specific language governing permissions and
+	# limitations under the License.
+-%>
+if err := d.Set("labels", nil); err != nil {
+    return res, fmt.Errorf("Error ignoring Removed fields for AlertPolicy: %s", err)
+}
+return res, nil