Internal Server Error (500) on REST API CQL content search for Subpage when the Parent Page does not have a Child Page

Issue Summary

Internal Server Error (500) on REST API CQL content search for Subpage when the Parent Page does not have a Child Page

Steps to Reproduce

1. Get a Page ID of a Parent Page that does not have any Child Page.
2. Request for the Subpage of the Parent Page:

   <CONFLUENCE_BASE_URL>/rest/api/content/search?cql=parent=<PARENT_PAGE_ID>
   

Expected Results

Response (as in Confluence 6.15.x):

{"results":[],"start":0,"limit":25,"size":0,"_links":{"self":"http://localhost:8090/confluence/rest/api/content/search?cql=parent=8290306","base":"http://localhost:8090/confluence","context":"/confluence"}}

Actual Results

Response (as in Confluence 7.1.x):

{"statusCode":500,"message":"","reason":"Internal Server Error"}

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available