Export of space/page to PDF fails when content by label macro used inside section macro

Issue Summary

For old/legacy editor pages, export of space/page to PDF fails when content by label macro is used inside section macro.

Steps to Reproduce

1. Step 1: Create an old/legacy editor page using a legacy editor template.
2. Step 2: Insert the "Section" macro into the page.
3. Step 3: Insert a "Content by Label" macro inside the "Section" macro by adding some labels.
4. Step 4: Save and Publish the Page.
5. Step 5: Try to export the page or the whole space into PDF format.

Expected Results

PDF should be ready to download like below:

Actual Results

The PDF export fails with an error "We couldn't complete your export. Exception thrown while rendering the page 'null' to the PDF document /data/confluence/home/temp/XXXXXXXXX" like below:

The below exception is thrown in the Splunk logs:

Caused by: java.lang.NullPointerException:

Logger:

com.atlassian.confluence.extra.flyingpdf.PdfExportTaskRunnerImpl

Workaround

At the moment, remove the "Section" macro and use only the "Content by Label" macro in the old/legacy editor.