Fixed the following.

app/finders/pipelines_finder.rb

@@ -88,8 +88,9 @@ class PipelinesFinder
   end
 
   def by_yaml_errors(items)
-    if params[:yaml_errors].present? 
-      if params[:yaml_errors]
+    flg = Gitlab::Utils.to_boolean(params[:yaml_errors])
+    if flg.present?
+      if flg
         items.where("yaml_errors IS NOT NULL")
       else
         items.where("yaml_errors IS NULL")
@@ -102,7 +103,7 @@ class PipelinesFinder
   def order_and_sort(items)
     if params[:order_by].present? && params[:sort].present? && 
         items.column_names.include?(params[:order_by]) && 
-        (params[:sort].casecmp('ASC') || params[:sort].casecmp('DESC'))
+        params[:sort] =~ /\A(ASC|DESC)\Z/i
       items.reorder(params[:order_by] => params[:sort])
     else
       items.reorder(id: :desc)

spec/finders/pipelines_finder_spec.rb

@@ -13,6 +13,17 @@ describe PipelinesFinder do
   let!(:canceled_pipeline)    { create(:ci_pipeline, project: project, user: user, created_at:  2.minutes.ago, status: 'canceled') }
   let!(:skipped_pipeline)     { create(:ci_pipeline, project: project, user: user, created_at:  1.minute.ago,  status: 'skipped') }
   let!(:yaml_errors_pipeline) { create(:ci_pipeline, project: project, user: user, yaml_errors: 'Syntax error') }
+  let(:dummy_pipelines) do
+    [tag_pipeline,
+    created_pipeline,
+    pending_pipeline,
+    running_pipeline,
+    success_pipeline,
+    failed_pipeline,
+    canceled_pipeline,
+    skipped_pipeline,
+    yaml_errors_pipeline]
+  end
 
   subject { described_class.new(project, params).execute }
 
@@ -21,29 +32,12 @@ describe PipelinesFinder do
       let(:params) { {} }
 
       it 'selects all pipelines' do
-        expect(subject.count).to be 9
-        expect(subject).to include tag_pipeline
-        expect(subject).to include created_pipeline
-        expect(subject).to include pending_pipeline
-        expect(subject).to include running_pipeline
-        expect(subject).to include success_pipeline
-        expect(subject).to include failed_pipeline
-        expect(subject).to include canceled_pipeline
-        expect(subject).to include skipped_pipeline
-        expect(subject).to include yaml_errors_pipeline
+        expect(subject.count).to be dummy_pipelines.count
+        expect(subject).to match_array(dummy_pipelines)
       end
 
       it 'orders in descending order on ID' do
-        expected_ids = [tag_pipeline.id, 
-                        created_pipeline.id, 
-                        pending_pipeline.id,
-                        running_pipeline.id,
-                        success_pipeline.id,
-                        failed_pipeline.id,
-                        canceled_pipeline.id,
-                        skipped_pipeline.id,
-                        yaml_errors_pipeline.id].sort.reverse
-        expect(subject.map(&:id)).to eq expected_ids
+        expect(subject.map(&:id)).to eq dummy_pipelines.map(&:id).sort.reverse
       end
     end
 
@@ -210,6 +204,15 @@ describe PipelinesFinder do
           expect(subject).to include skipped_pipeline
         end
       end
+
+      context 'when an argument is invalid' do
+        let(:params) { { yaml_errors: "UnexpectedValue" } }
+
+        it 'selects all pipelines' do
+          expect(subject.count).to be dummy_pipelines.count
+          expect(subject).to match_array(dummy_pipelines)
+        end
+      end
     end
 
     context 'when a order_by and sort are passed' do
@@ -230,6 +233,22 @@ describe PipelinesFinder do
           expect(subject.last).to eq(tag_pipeline)
         end
       end
+
+      context 'when order_by does not exist' do
+        let(:params) { { order_by: 'abnormal_column', sort: 'desc' } }
+
+        it 'sorts by default' do
+          expect(subject.map(&:id)).to eq dummy_pipelines.map(&:id).sort.reverse
+        end
+      end
+
+      context 'when sort does not exist' do
+        let(:params) { { order_by: 'created_at', sort: 'abnormal_sort' } }
+
+        it 'sorts by default' do
+          expect(subject.map(&:id)).to eq dummy_pipelines.map(&:id).sort.reverse
+        end
+      end
     end
   end
 end