Add support for #cast_values to EmptyResult

This method was introduced in 4.2, where it is used for type casting.

lib/active_record/connection_adapters/nulldb_adapter/empty_result.rb

@@ -13,6 +13,10 @@ def column_types
     def columns
       @columns ||= []
     end
+
+    def cast_values(type_overrides = nil)
+      rows
+    end
   end
 
 end

spec/nulldb_spec.rb

@@ -323,3 +323,11 @@ def should_have_column(klass, col_name, col_type)
     }.to_not raise_error
   end
 end
+
+describe ActiveRecord::ConnectionAdapters::NullDBAdapter::EmptyResult do
+  it "should return an empty array from #cast_values" do
+    result = described_class.new
+    expect( result.cast_values ).to be_a Array
+    expect( result.cast_values ).to be_empty
+  end
+end