On any page at http://en.wikipedia.beta.wmflabs.org/

Make an edit

Click Review your changes

User sees a modal dialog saying "Error loading data from server: error."

fatal log shows

[2014-06-16 14:57:25] Fatal error: Call to a member function get() on a non-object at /srv/common-local/php-master/includes/api/ApiQueryRevisions.php on line 629
Server: deployment-apache02
Method: POST
URL: http://en.wikipedia.beta.wmflabs.org/w/api.php
Cookie: enwiki-gettingStartedUserId=kJSYCjZCvJa3o9xl48ODXiGk1DaduG2m; centralnotice_bucket=1-4.2; centralauth_LoggedOut=1402329725; ve-beta-welcome-dialog=1; edittoolscharsubset=0; optin=beta; GeoIP=US:Tucson:32.2217:-110.9265:v4; uls-previous-languages=%5B%22en%22%5D; mediaWiki.user.sessionId=y0AhKxKUggdcyUd7KMOLw6Bx8JuBJTqT; enwikiUserID=54; enwikiUserName=Cmcmahon; enwikiSession=090850308740c4e1214d05399aa6d221; centralauth_User=Cmcmahon; centralauth_Session=d47cf247a4d3ea1081576f3520609ffe
Backtrace:
#0 /srv/common-local/php-master/includes/api/ApiQueryRevisions.php(629): ApiQueryRevisions::extractRowInfo()
#1 /srv/common-local/php-master/includes/api/ApiQueryRevisions.php(402): ApiQueryRevisions->extractRowInfo(Object(stdClass))
#2 /srv/common-local/php-master/includes/api/ApiQuery.php(282): ApiQueryRevisions->execute()
#3 /srv/common-local/php-master/includes/api/ApiMain.php(908): ApiQuery->execute()
#4 /srv/common-local/php-master/includes/api/ApiMain.php(332): ApiMain->executeAction()
#5 /srv/common-local/php-master/extensions/VisualEditor/ApiVisualEditor.php(230): ApiMain->execute()
#6 /srv/common-local/php-master/extensions/VisualEditor/ApiVisualEditor.php(501): ApiVisualEditor->diffWikitext(Object(Title), 'Starting a new ...')
#7 /srv/common-local/php-master/includes/api/ApiMain.php(908): ApiVisualEditor->execute()
#8 /srv/common-local/php-master/includes/api/ApiMain.php(363): ApiMain->executeAction()
#9 /srv/common-local/php-master/includes/api/ApiMain.php(334): ApiMain->executeActionWithErrorHandling()
#10 /srv/common-local/php-master/api.php(85): ApiMain->execute()
#11 /srv/common-local/w/api.php(3): require('/srv/common-loc...')
#12 {main}
[2014-06-16 14:57:25]

Version: unspecified
Severity: major