From ae322aad90cefa78b26fd6f10b8f743b3190d141 Mon Sep 17 00:00:00 2001
From: Koza <kiskoza@gmail.com>
Date: Thu, 19 Oct 2023 15:56:06 +0200
Subject: Fix frozen string error for scatter series with non-default marker

---
 lib/axlsx/drawing/scatter_series.rb | 2 +-
 test/drawing/tc_scatter_series.rb   | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/lib/axlsx/drawing/scatter_series.rb b/lib/axlsx/drawing/scatter_series.rb
index 865c6f85..ffff81f5 100644
--- a/lib/axlsx/drawing/scatter_series.rb
+++ b/lib/axlsx/drawing/scatter_series.rb
@@ -121,7 +121,7 @@ module Axlsx
       if !@show_marker
         '<c:symbol val="none"/>'
       elsif @marker_symbol != :default
-        '<c:symbol val="' << @marker_symbol.to_s << '"/>'
+        +'<c:symbol val="' << @marker_symbol.to_s << '"/>'
       end.to_s
     end
   end
diff --git a/test/drawing/tc_scatter_series.rb b/test/drawing/tc_scatter_series.rb
index 26ed01ea..0bfb2413 100644
--- a/test/drawing/tc_scatter_series.rb
+++ b/test/drawing/tc_scatter_series.rb
@@ -60,6 +60,15 @@ class TestScatterSeries < Test::Unit::TestCase
     assert_equal(1, doc.xpath("//a:ln[@w='#{@series.ln_width}']").length)
   end
 
+  def test_to_xml_string_non_default_marker
+    @chart = @ws.add_chart Axlsx::ScatterChart, title: 'Line chart', scatter_style: :smoothMarker
+    @series = @chart.add_series xData: [1, 2, 4], yData: [1, 3, 9]
+    @series.marker_symbol = :circle
+    doc = Nokogiri::XML(@chart.to_xml_string)
+
+    assert_equal(1, doc.xpath("//c:symbol[@val='#{@series.marker_symbol}']").length)
+  end
+
   def test_false_show_marker
     @chart = @ws.add_chart Axlsx::ScatterChart, title: 'Smooth Chart', scatter_style: :smoothMarker
     @series = @chart.add_series xData: [1, 2, 4], yData: [1, 3, 9]
-- 
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