For some user commit pairs the "show older changes" link in an audit view does always brings up the unhandled exception message box with:
```
Argument 1 passed to idx() must be of the type array, null given, called in /home/phabricator/phabricator/src/applications/audit/view/PhabricatorAuditTransactionView.php on line 99 and defined
```
The redacted stack trace for one such occurrence:
```
[2015-01-23 17:13:03] EXCEPTION: (InvalidArgumentException) Argument 1 passed to idx() must be of the type array, null given, called in /home/phabricator/phabricator/src/applications/audit/view/PhabricatorAuditTransactionView.php on line 99 and defined at [<phutil>/src/error/PhutilErrorHandler.php:200], referer: http://review.<site>/rRS151194
#0 PhutilErrorHandler::handleError(integer, string, string, integer, array) called at [<phutil>/src/utils/utils.php:36], referer: http://review.<site>/rRS151194
#1 idx(NULL, integer) called at [<phabricator>/src/applications/audit/view/PhabricatorAuditTransactionView.php:99], referer: http://review.<site>/rRS151194
#2 PhabricatorAuditTransactionView::renderTransactionContent(PhabricatorAuditTransaction) called at [<phabricator>/src/applications/transactions/view/PhabricatorApplicationTransactionView.php:496], referer: http://review.<site>/rRS151194
#3 PhabricatorApplicationTransactionView::renderEvent(PhabricatorAuditTransaction, array) called at [<phabricator>/src/applications/transactions/view/PhabricatorApplicationTransactionView.php:173], referer: http://review.<site>/rRS151194
#4 PhabricatorApplicationTransactionView::buildEvents(boolean) called at [<phabricator>/src/applications/transactions/view/PhabricatorApplicationTransactionView.php:219], referer: http://review.<site>/rRS151194
#5 PhabricatorApplicationTransactionView::buildPHUITimelineView(boolean) called at [<phabricator>/src/applications/transactions/controller/PhabricatorApplicationTransactionShowOlderController.php:46], referer: http://review.<site>/rRS151194
#6 PhabricatorApplicationTransactionShowOlderController::handleRequest(AphrontRequest) called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:196], referer: http://review.<site>/rRS151194
#7 AphrontApplicationConfiguration::processRequest(AphrontRequest, PhutilDeferredLog, AphrontPHPHTTPSink) called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:121], referer: http://review.<site>/rRS151194
#8 AphrontApplicationConfiguration::runHTTPRequest(AphrontPHPHTTPSink) called at [<phabricator>/webroot/index.php:19], referer: http://review.<site>/rRS151194
```
Other users seem to see all comments for the particular commits without any problems but have problems on others. In the cases found the users with problems apparently had made comments which were hidden behind "show older changes".
This might be similar in nature to the problem in T6720 which was apparently fixed by D10935.
We updated to Phabricator HEAD (rP30eea5e93680) but the problem persists.