NullPointerException prevents page update

Issue

When attempting to update certain pages, they fail with "Paragraph delete operation failed" and the error [1] below is logged in the error.log. This error occurs on sites that are using Multi-Site Manager (MSM) where a Form component is on the page.

[1]

java.lang.NullPointerException: null
	at com.day.cq.wcm.msm.impl.postprocessing.GhostPostProcessor.process(GhostPostProcessor.java:86)
	at org.apache.sling.servlets.post.AbstractPostOperation.run(AbstractPostOperation.java:97)
	at org.apache.sling.servlets.post.impl.SlingPostServlet.doPost(SlingPostServlet.java:199)

Environment

AEM 6.2

Cause

Known product bug CQ-44298 / NPR-20855.

Resolution

Install the latest AEM 6.2 Cumulative Fix pack. The fix is included in the January 2018 fix pack CFP11.