"Cannot access empty property" causes cron failure

Running cron had been failing for 24 hours with a time limit exceeded message displayed in watchdog. Running cron from the command line resulted in this error message: (more or less, forgot to grab a copy)

Fatal error: Cannot access empty property in /www/home/public_html/default/modules/feedapi_mapper/mappers/feedapi_mapper_date.inc on line 117

Examining mappers/feedapi_mapper_date.inc line 116-118 reads:

  if (!isset($node->{$field_name})) {
    $node->$field_name = array($date->value);
  }

I believe it should be:

  if (!isset($node->{$field_name})) {
    $node->field_name = array($date->value);
  }

(eliminating the $ before field_name on line 117)

I believe it has been this line of code causing my cron run to fail routinely on perhaps badly formatted RSS entries, but instead of handling the error the entire cron run fails. In the past I would manually update every RSS feed until I got past the offending entry.

Making the change above allowed my cron to complete for the first time in 24 hours so I'm quite confident this little $ has been the cause of my consistently broken website. *crosses fingers*

Since I have had this problem many times I am curious if others have experienced it. I do believe the code structure used worked in PHP4, but is no longer workable with PHP5.