backport fix for #2343 provide a fallback value for base-font-size

CHANGELOG.adoc

@@ -7,6 +7,10 @@ For a detailed view of what has changed, refer to the {url-repo}/commits/main[co
 
 == Unreleased
 
+Improvements::
+
+* provide a fallback value for `base-font-size` when loading theme (#2343)
+
 Bug Fixes::
 
 * fix crash when smallcaps text transform is applied to a phrase (#2339)

lib/asciidoctor/pdf/theme_loader.rb

@@ -83,6 +83,7 @@ def self.load_theme theme_name = nil, theme_dir = nil
             theme_data.base_text_align ||= 'left'
             theme_data.base_line_height ||= 1
             theme_data.base_font_color ||= '000000'
+            theme_data.base_font_size ||= 12
             theme_data.code_font_family ||= (theme_data.codespan_font_family || 'Courier')
             theme_data.conum_font_family ||= (theme_data.codespan_font_family || 'Courier')
             if (heading_font_family = theme_data.heading_font_family)

spec/theme_loader_spec.rb

@@ -781,7 +781,7 @@
           theme = subject.load_theme (File.basename theme_path), (File.dirname theme_path)
           (expect theme.base_font_family).to eql 'Times-Roman'
           (expect theme.heading_font_family).to eql 'Times-Roman'
-          (expect theme.base_font_size).to be_nil
+          (expect theme.base_font_size).to be 12
         end
       end
     end
@@ -889,9 +889,10 @@
       (expect theme.base_text_align).to eql 'left'
       (expect theme.base_line_height).to be 1
       (expect theme.base_font_color).to eql '000000'
+      (expect theme.base_font_size).to be 12
       (expect theme.code_font_family).to eql 'Courier'
       (expect theme.conum_font_family).to eql 'Courier'
-      (expect theme.to_h.keys).to have_size 6
+      (expect theme.to_h.keys).to have_size 7
     end
 
     it 'should link code and conum font family to codespan font family by default' do