resolves #3118 fix crash if stem block is empty (PR #3119)

4 files changed, 31 insertions, 12 deletions

diff --git a/CHANGELOG.adoc b/CHANGELOG.adoc
index f4487f3a..e135961d 100644
--- a/CHANGELOG.adoc
+++ b/CHANGELOG.adoc
@@ -103,6 +103,7 @@ Bug Fixes::
   * apply header subs to doctitle value when assigning it back to the doctitle document attribute (#3106)
   * don't fail if value of pygments-style attribute is not recognized; gracefully fallback to default style (#2106)
   * do not alter the $LOAD_PATH (#2764)
+  * fix crash if stem block is empty (#3118)
   * remove conditional comment for IE in output of built-in HTML converter; fixes sidebar table of contents (#2983)
   * fix styling of source blocks with linenums enabled when using prettify as syntax highlighter (#640)
   * update default stylesheet to support prettify themes (#3020)
diff --git a/lib/asciidoctor/converter/docbook5.rb b/lib/asciidoctor/converter/docbook5.rb
index c07a423e..a87e1ca5 100644
--- a/lib/asciidoctor/converter/docbook5.rb
+++ b/lib/asciidoctor/converter/docbook5.rb
@@ -256,10 +256,10 @@ class Converter::DocBook5Converter < Converter::Base
   def stem node
     if (idx = node.subs.index :specialcharacters)
       node.subs.delete_at idx
-      equation = node.content
+      equation = node.content || ''
       idx > 0 ? (node.subs.insert idx, :specialcharacters) : (node.subs.unshift :specialcharacters)
     else
-      equation = node.content
+      equation = node.content || ''
     end
     if node.style == 'asciimath'
       # NOTE fop requires jeuclid to process mathml markup
diff --git a/lib/asciidoctor/converter/html5.rb b/lib/asciidoctor/converter/html5.rb
index f32c4567..e3d0467d 100644
--- a/lib/asciidoctor/converter/html5.rb
+++ b/lib/asciidoctor/converter/html5.rb
@@ -620,17 +620,17 @@ Your browser does not support the audio tag.
     id_attribute = node.id ? %( id="#{node.id}") : ''
     title_element = node.title? ? %(<div class="title">#{node.title}</div>\n) : ''
     open, close = BLOCK_MATH_DELIMITERS[style = node.style.to_sym]
-    equation = node.content
-
-    if style == :asciimath && (equation.include? LF)
-      br = %(<br#{@void_element_slash}>#{LF})
-      equation = equation.gsub(StemBreakRx) { %(#{close}#{br * ($&.count LF)}#{open}) }
-    end
-
-    unless (equation.start_with? open) && (equation.end_with? close)
-      equation = %(#{open}#{equation}#{close})
+    if (equation = node.content)
+      if style == :asciimath && (equation.include? LF)
+        br = %(<br#{@void_element_slash}>#{LF})
+        equation = equation.gsub(StemBreakRx) { %(#{close}#{br * ($&.count LF)}#{open}) }
+      end
+      unless (equation.start_with? open) && (equation.end_with? close)
+        equation = %(#{open}#{equation}#{close})
+      end
+    else
+      equation = ''
     end
-
     %(<div#{id_attribute} class="stemblock#{(role = node.role) ? " #{role}" : ''}">
 #{title_element}<div class="content">
 #{equation}
diff --git a/test/blocks_test.rb b/test/blocks_test.rb
index aab7341d..f1906a37 100644
--- a/test/blocks_test.rb
+++ b/test/blocks_test.rb
@@ -1561,6 +1561,17 @@ context 'Blocks' do
   end
 
   context 'Math blocks' do
+    test 'should not crash when converting to HTML if stem block is empty' do
+      input = <<~'EOS'
+      [stem]
+      ++++
+      ++++
+      EOS
+
+      output = convert_string_to_embedded input
+      assert_css '.stemblock', output, 1
+    end
+
     test 'should add LaTeX math delimiters around latexmath block content' do
       input = <<~'EOS'
       [latexmath]
@@ -1725,12 +1736,19 @@ context 'Blocks' do
       ++++
       x+b/(2a)<+-sqrt((b^2)/(4a^2)-c/a)
       ++++
+
+      [asciimath]
+      ++++
+      ++++
       EOS
 
       expect = <<~'EOS'.chop
       <informalequation>
       <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>x</mml:mi><mml:mo>+</mml:mo><mml:mfrac><mml:mi>b</mml:mi><mml:mrow><mml:mn>2</mml:mn><mml:mi>a</mml:mi></mml:mrow></mml:mfrac><mml:mo>&lt;</mml:mo><mml:mo>&#xB1;</mml:mo><mml:msqrt><mml:mrow><mml:mfrac><mml:msup><mml:mi>b</mml:mi><mml:mn>2</mml:mn></mml:msup><mml:mrow><mml:mn>4</mml:mn><mml:msup><mml:mi>a</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:mfrac><mml:mo>&#x2212;</mml:mo><mml:mfrac><mml:mi>c</mml:mi><mml:mi>a</mml:mi></mml:mfrac></mml:mrow></mml:msqrt></mml:math>
       </informalequation>
+      <informalequation>
+      <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"></mml:math>
+      </informalequation>
       EOS
 
       using_memory_logger do |logger|