Set default before_or_after for keyset conditions

and add relevant specs

lib/gitlab/graphql/connections/keyset/conditions/base_condition.rb

@@ -8,6 +8,8 @@ module Gitlab
           class BaseCondition
             def initialize(arel_table, order_list, values, operators, before_or_after)
               @arel_table, @order_list, @values, @operators, @before_or_after = arel_table, order_list, values, operators, before_or_after
+
+              @before_or_after = :after unless [:after, :before].include?(@before_or_after)
             end
 
             def build

spec/lib/gitlab/graphql/connections/keyset/conditions/not_null_condition_spec.rb

@@ -28,7 +28,7 @@ describe Gitlab::Graphql::Connections::Keyset::Conditions::NotNullCondition do
       let(:order_list) { %w(relative_position id) }
       let(:values)     { [1500, 500] }
 
-      context 'when :after' do
+      shared_examples ':after condition' do
         it 'generates :after sql' do
           expected_sql = <<~SQL
             ("issues"."relative_position" > 1500)
@@ -44,6 +44,10 @@ describe Gitlab::Graphql::Connections::Keyset::Conditions::NotNullCondition do
         end
       end
 
+      context 'when :after' do
+        it_behaves_like ':after condition'
+      end
+
       context 'when :before' do
         let(:before_or_after) { :before }
 
@@ -60,6 +64,12 @@ describe Gitlab::Graphql::Connections::Keyset::Conditions::NotNullCondition do
           expect(condition.build.squish).to eq expected_sql.squish
         end
       end
+
+      context 'when :foo' do
+        let(:before_or_after) { :foo }
+
+        it_behaves_like ':after condition'
+      end
     end
   end
 end

spec/lib/gitlab/graphql/connections/keyset/conditions/null_condition_spec.rb

@@ -13,20 +13,24 @@ describe Gitlab::Graphql::Connections::Keyset::Conditions::NullCondition do
       let(:arel_table) { Issue.arel_table }
       let(:order_list) { %w(relative_position id) }
 
-      context 'when :after' do
+      shared_examples ':after condition' do
         it 'generates sql' do
           expected_sql = <<~SQL
-          (
-            "issues"."relative_position" IS NULL
-            AND
-            "issues"."id" > 500
-          )
+            (
+              "issues"."relative_position" IS NULL
+              AND
+              "issues"."id" > 500
+            )
           SQL
 
           expect(condition.build.squish).to eq expected_sql.squish
         end
       end
 
+      context 'when :after' do
+        it_behaves_like ':after condition'
+      end
+
       context 'when :before' do
         let(:before_or_after) { :before }
 
@@ -43,6 +47,12 @@ describe Gitlab::Graphql::Connections::Keyset::Conditions::NullCondition do
           expect(condition.build.squish).to eq expected_sql.squish
         end
       end
+
+      context 'when :foo' do
+        let(:before_or_after) { :foo }
+
+        it_behaves_like ':after condition'
+      end
     end
   end
 end