When someone tries to log on with invalid credentials, a record is inserted in the phabricator_user.user_log table with action = login-fail.
The session value of this record is set to null in this case.
When you open the People → Activity Logs screen, you will see an exception because of this.
Stack trace
[Sat Jul 15 14:29:22.840573 2023] [php:notice] [2001:db8:0:f101::1:37608] [2023-07-15 12:29:22] EXCEPTION: (RuntimeException) substr(): Passing null to parameter #1 ($string) of type string is deprecated at [<arcanist>/src/error/PhutilErrorHandler.php:261] [Sat Jul 15 14:29:22.841072 2023] [php:notice] [2001:db8:0:f101::1:37608] arcanist(head=master, ref.master=6e4947b55f09), diagram(head=master, ref.master=9031a4f716a0), example(), phorge(head=master, ref.master=f7dd8f579a36, custom=1) [Sat Jul 15 14:29:22.841079 2023] [php:notice] [2001:db8:0:f101::1:37608] #0 <#2> PhutilErrorHandler::handleError(integer, string, string, integer) called at [<arcanist>/src/error/PhutilErrorHandler.php:261] [Sat Jul 15 14:29:22.841082 2023] [php:notice] [2001:db8:0:f101::1:37608] #1 <#2> substr(NULL, integer, integer) called at [<phorge>/src/applications/people/view/PhabricatorUserLogView.php:39] [Sat Jul 15 14:29:22.841093 2023] [php:notice] [2001:db8:0:f101::1:37608] #2 <#2> phutil_escape_html(array) called at [<phorge>/src/infrastructure/markup/render.php:97] [Sat Jul 15 14:29:22.841095 2023] [php:notice] [2001:db8:0:f101::1:37608] #3 <#2> phutil_tag(string, array, array) called at [<phorge>/src/infrastructure/javelin/markup.php:70] [Sat Jul 15 14:29:22.841097 2023] [php:notice] [2001:db8:0:f101::1:37608] #4 <#2> javelin_tag(string, array, array) called at [<phorge>/src/view/AphrontTagView.php:158] [Sat Jul 15 14:29:22.841100 2023] [php:notice] [2001:db8:0:f101::1:37608] #5 <#2> AphrontTagView::render() called at [<phorge>/src/view/AphrontView.php:222] [Sat Jul 15 14:29:22.841102 2023] [php:notice] [2001:db8:0:f101::1:37608] #6 <#2> AphrontView::producePhutilSafeHTML() called at [<phorge>/src/infrastructure/markup/render.php:115] [Sat Jul 15 14:29:22.841104 2023] [php:notice] [2001:db8:0:f101::1:37608] #7 <#2> phutil_escape_html(PHUIObjectBoxView) called at [<phorge>/src/infrastructure/markup/render.php:139] [Sat Jul 15 14:29:22.841107 2023] [php:notice] [2001:db8:0:f101::1:37608] #8 <#2> phutil_escape_html(array) called at [<phorge>/src/infrastructure/markup/render.php:171] [Sat Jul 15 14:29:22.841109 2023] [php:notice] [2001:db8:0:f101::1:37608] #9 <#2> phutil_implode_html(string, array) called at [<phorge>/src/view/page/PhabricatorBarePageView.php:58] [Sat Jul 15 14:29:22.841111 2023] [php:notice] [2001:db8:0:f101::1:37608] #10 <#2> PhabricatorBarePageView::willRenderPage() called at [<phorge>/src/view/page/PhabricatorStandardPageView.php:216] [Sat Jul 15 14:29:22.841113 2023] [php:notice] [2001:db8:0:f101::1:37608] #11 <#2> PhabricatorStandardPageView::willRenderPage() called at [<phorge>/src/view/page/AphrontPageView.php:46] [Sat Jul 15 14:29:22.841115 2023] [php:notice] [2001:db8:0:f101::1:37608] #12 <#2> AphrontPageView::render() called at [<phorge>/src/view/page/PhabricatorStandardPageView.php:904] [Sat Jul 15 14:29:22.841118 2023] [php:notice] [2001:db8:0:f101::1:37608] #13 <#2> PhabricatorStandardPageView::produceAphrontResponse() called at [<phorge>/src/aphront/configuration/AphrontApplicationConfiguration.php:722] [Sat Jul 15 14:29:22.841120 2023] [php:notice] [2001:db8:0:f101::1:37608] #14 <#2> AphrontApplicationConfiguration::produceResponse(AphrontRequest, PhabricatorStandardPageView) called at [<phorge>/src/aphront/configuration/AphrontApplicationConfiguration.php:299] [Sat Jul 15 14:29:22.841122 2023] [php:notice] [2001:db8:0:f101::1:37608] #15 phlog(RuntimeException) called at [<phorge>/src/aphront/handler/PhabricatorDefaultRequestExceptionHandler.php:41] [Sat Jul 15 14:29:22.841125 2023] [php:notice] [2001:db8:0:f101::1:37608] #16 PhabricatorDefaultRequestExceptionHandler::handleRequestThrowable(AphrontRequest, RuntimeException) called at [<phorge>/src/aphront/configuration/AphrontApplicationConfiguration.php:751] [Sat Jul 15 14:29:22.841127 2023] [php:notice] [2001:db8:0:f101::1:37608] #17 AphrontApplicationConfiguration::handleThrowable(RuntimeException) called at [<phorge>/src/aphront/configuration/AphrontApplicationConfiguration.php:337] [Sat Jul 15 14:29:22.841129 2023] [php:notice] [2001:db8:0:f101::1:37608] #18 AphrontApplicationConfiguration::processRequest(AphrontRequest, PhutilDeferredLog, AphrontPHPHTTPSink, MultimeterControl) called at [<phorge>/src/aphront/configuration/AphrontApplicationConfiguration.php:203] [Sat Jul 15 14:29:22.841135 2023] [php:notice] [2001:db8:0:f101::1:37608] #19 AphrontApplicationConfiguration::runHTTPRequest(AphrontPHPHTTPSink) called at [<phorge>/webroot/index.php:35]