FIX: ensures tags/categories are present (#28230)

Prior to this fix the query in stalled_topic_finder would assume that tags/categories would be nil or an array of ids. However it can be an empty array, in this case the query will not return results.

plugins/automation/spec/lib/discourse_automation/stalled_topic_finder_spec.rb

@@ -56,6 +56,14 @@ describe DiscourseAutomation::StalledTopicFinder do
         described_class.call(2.hours.from_now, tags: [tag_1.name]).map(&:id),
       ).to contain_exactly(topic_1.id)
     end
+
+    it "still finds topics if tags is empty" do
+      create_post(topic: topic_4, user: user)
+
+      expect(described_class.call(2.hours.from_now, tags: []).map(&:id)).to contain_exactly(
+        topic_4.id,
+      )
+    end
   end
 
   describe "filter by categories" do
@@ -80,6 +88,14 @@ describe DiscourseAutomation::StalledTopicFinder do
         described_class.call(2.hours.from_now, categories: [category_1.id]).map(&:id),
       ).to contain_exactly(topic_1.id)
     end
+
+    it "still finds topics if categories is empty" do
+      create_post(topic: topic_1, user: user)
+
+      expect(described_class.call(2.hours.from_now, categories: []).map(&:id)).to contain_exactly(
+        topic_1.id,
+      )
+    end
   end
 
   describe "filter recent topic owner replies" do