Ignore deleted devices while showing the App usage report

spec/models/app_usage_spec.rb

@@ -7,4 +7,13 @@ RSpec.describe AppUsage, type: :model do
   it { should validate_presence_of :usage_duration_in_seconds } 
   it { should validate_presence_of :used_on } 
   it { should belong_to :device }
+
+  context "App Usage report" do
+    let!(:app_usage) { create(:app_usage,device_id: nil) }
+    it "Ignore Deleted devices" do
+      app_usage = AppUsage.app_usages_per_device_app_day
+      expect(app_usage).to be_empty
+    end
+
+  end
 end