Uncaught Error:  operator not supported for strings in /wp-content/plugins/civicrm/civicrm/CRM/Report/Form/Contribute/Summary.php:580
Don't know whether this started with Civi 4.7.19, WP 4.8, or something else -- but now I get this 500 error whenever I try to run a Contribution Summary (Reports / Contribution Reports).
Other Civi summary reports (e.g. Constituent Summary, Event Participants List) run as expected. Other Civi Contribution reports also run as expected. It seems Contribution Summary is our only misbehaving report.
I've disabled all plugins other than CiviCRM and activated Twenty Seventeen theme, but that doesn't stop the 500 error.
Stack trace: [13-Jun-2017 08:57:17 America/New_York] PHP Fatal error: Uncaught Error:  operator not supported for strings in /wp-content/plugins/civicrm/civicrm/CRM/Report/Form/Contribute/Summary.php:580 Jun 13, 12:53:49 PHP Warning: Failed to send an email, wp_mail() returned FALSE in /wp-content/plugins/error-log-monitor/Elm/Plugin.php on line 200 5 [REDACTED] in /wp-content/plugins/civicrm/civicrm/CRM/Report/Form/Contribute/Summary.php on line 580 4 /wp-content/plugins/civicrm/civicrm/CRM/Core/QuickForm/Action/Submit.php(74): CRM_Core_Form->mainProcess() 3 /wp-content/plugins/civicrm/civicrm/CRM/Core/Form.php(447): CRM_Report_Form_Contribute_Summary->postProcess() 2 /wp-content/plugins/civicrm/civicrm/CRM/Report/Form/Contribute/Summary.php(756): CRM_Report_Form->postProcess() 1 /wp-content/plugins/civicrm/civicrm/CRM/Report/Form.php(3249): CRM_Report_Form->buildQuery() 0 /wp-content/plugins/civicrm/civicrm/CRM/Report/Form.php(2626): CRM_Report_Form_Contribute_Summary->groupBy()
It is possible we've had this problem since well before the current Civi and WordPress iterations were released/installed, but hadn't noticed it before because we're still somewhat new to Civi.
I activated debugging and backtracing, but no error info displayed when running Contribution Summary.
I assume Contribution Summary is working fine for everyone else. What should I try next?