Use nullify_if_blank for cluster_platforms_kubernetes.namespace

app/models/clusters/platforms/kubernetes.rb

@@ -7,6 +7,7 @@ module Clusters
       include EnumWithNil
       include AfterCommitQueue
       include ReactiveCaching
+      include NullifyIfBlank
 
       RESERVED_NAMESPACES = %w(gitlab-managed-apps).freeze
 
@@ -25,7 +26,6 @@ module Clusters
         key: Settings.attr_encrypted_db_key_base_truncated,
         algorithm: 'aes-256-cbc'
 
-      before_validation :nullify_blank_namespace
       before_validation :enforce_namespace_to_lower_case
       before_validation :enforce_ca_whitespace_trimming
 
@@ -64,6 +64,8 @@ module Clusters
 
       default_value_for :authorization_type, :rbac
 
+      nullify_if_blank :namespace
+
       def predefined_variables(project:, environment_name:, kubernetes_namespace: nil)
         Gitlab::Ci::Variables::Collection.new.tap do |variables|
           variables.append(key: 'KUBE_URL', value: api_url)
@@ -255,10 +257,6 @@ module Clusters
         true
       end
 
-      def nullify_blank_namespace
-        self.namespace = nil if namespace.blank?
-      end
-
       def extract_relevant_pod_data(pods)
         pods.map do |pod|
           {

spec/models/clusters/platforms/kubernetes_spec.rb

@@ -17,6 +17,8 @@ RSpec.describe Clusters::Platforms::Kubernetes do
   it { is_expected.to delegate_method(:enabled?).to(:cluster) }
   it { is_expected.to delegate_method(:provided_by_user?).to(:cluster) }
 
+  it { is_expected.to nullify_if_blank(:namespace) }
+
   it_behaves_like 'having unique enum values'
 
   describe 'before_validation' do
@@ -29,14 +31,6 @@ RSpec.describe Clusters::Platforms::Kubernetes do
         expect(kubernetes.namespace).to eq('abc')
       end
     end
-
-    context 'when namespace is blank' do
-      let(:namespace) { '' }
-
-      it 'nullifies the namespace' do
-        expect(kubernetes.namespace).to be_nil
-      end
-    end
   end
 
   describe 'validation' do