Fix FrozenError for blank case tag with multiple expression when tag (#1340)

lib/liquid/tags/case.rb

@@ -22,8 +22,11 @@ module Liquid
       body = new_body
       body = @blocks.last.attachment while parse_body(body, tokens)
       @blocks.each do |condition|
-        condition.attachment.remove_blank_strings if blank?
-        condition.attachment.freeze
+        body = condition.attachment
+        unless body.frozen?
+          body.remove_blank_strings if blank?
+          body.freeze
+        end
       end
     end
 

test/integration/tags/standard_tag_test.rb

@@ -213,6 +213,11 @@ class StandardTagTest < Minitest::Test
     assert_template_result('', code, 'condition' => 'something else')
   end
 
+  def test_case_when_comma_and_blank_body
+    code = '{% case condition %}{% when 1, 2 %} {% assign r = "result" %} {% endcase %}{{ r }}'
+    assert_template_result('result', code, 'condition' => 2)
+  end
+
   def test_assign
     assert_template_result('variable', '{% assign a = "variable"%}{{a}}')
   end