Don’t crash with empty list marker strings

Fix #1883.

tests/css/test_counters.py

@@ -518,6 +518,11 @@ def test_list_style_types(style_type, values):
     assert li_4.children[0].children[0].children[0].text == values[3]
 
 
+def test_list_style_type_empty_string():
+    # Test regression: https://github.com/Kozea/WeasyPrint/issues/1883
+    render_pages('<ul><li style="list-style-type: \'\'">')
+
+
 def test_counter_set():
     page, = render_pages('''
       <style>

weasyprint/formatting_structure/build.py

@@ -345,11 +345,10 @@ def marker_to_box(element, state, parent_style, style_for, get_image_from_uri,
             counter_value = counter_values.get('list-item', [0])[-1]
             counter_type = style['list_style_type']
             # TODO: rtl numbered list has the dot on the left
-            marker_text = counter_style.render_marker(
-                counter_type, counter_value)
-            box = boxes.TextBox.anonymous_from(box, marker_text)
-            box.style['white_space'] = 'pre-wrap'
-            children.append(box)
+            if marker_text := counter_style.render_marker(counter_type, counter_value):
+                box = boxes.TextBox.anonymous_from(box, marker_text)
+                box.style['white_space'] = 'pre-wrap'
+                children.append(box)
 
     if not children:
         return