FIX: prevents crash in discourse_tagging with empty term (#8548)

lib/discourse_tagging.rb

@@ -222,7 +222,7 @@ module DiscourseTagging
 
     distinct_clause = if opts[:order_popularity]
       "DISTINCT ON (topic_count, name)"
-    elsif opts[:order_search_results]
+    elsif opts[:order_search_results] && opts[:term].present?
       "DISTINCT ON (lower(name) = lower(:cleaned_term), topic_count, name)"
     else
       ""
@@ -278,9 +278,7 @@ module DiscourseTagging
 
     term = opts[:term]
     if term.present?
-      term = term.gsub("_", "\\_")
-      clean_tag(term)
-      term.downcase!
+      term = term.gsub("_", "\\_").downcase
       builder.where("LOWER(name) LIKE :term")
       builder_params[:cleaned_term] = term
       builder_params[:term] = "%#{term}%"

spec/components/discourse_tagging_spec.rb

@@ -129,6 +129,16 @@ describe DiscourseTagging do
         end
       end
 
+      context 'empty term' do
+        it "works with an empty term" do
+          tags = DiscourseTagging.filter_allowed_tags(Guardian.new(user),
+            term: '',
+            order_search_results: true
+          ).map(&:name)
+          expect(sorted_tag_names(tags)).to eq(sorted_tag_names([tag1, tag2, tag3]))
+        end
+      end
+
       context 'tag synonyms' do
         fab!(:base_tag) { Fabricate(:tag, name: 'discourse') }
         fab!(:synonym) { Fabricate(:tag, name: 'discource', target_tag: base_tag) }