Issue: preg_match() expects parameter 2 to be string

ErrorException: preg_match() expects parameter 2 to be string, array given - vault/core/view/ui/proxy/xf.php:267 
Generated By: devilgoose, Yesterday at 11:20 PM

Stack Trace
#0 [internal function]: XenForo_Application::handlePhpError(2, 'preg_match() ex...', '/home/...', 267, Array)
#1 /vault/core/view/ui/proxy/xf.php(267): preg_match('#^[a-z_]+$#', Array, NULL)
#2 /vault/core/controller/ui/page/xf.php(92): vw_UI_Proxy_View_XF->standard_error(Array)
#3 /vault/core/controller/ui/page/xf.php(54): vw_UI_Page_Controller_XF->tags()
#4 /vault/core/controller/ui/stack/vw.php(271): vw_UI_Page_Controller_XF->execute()
#5 /library/vw/XenForo/ControllerPublic/Wiki.php(70): vw_UI_Stack_Controller->execute()
#6 /library/XenForo/FrontController.php(351): vw_XenForo_ControllerPublic_Wiki->actionIndex()
#7 /library/XenForo/FrontController.php(134): XenForo_FrontController->dispatch(Object(XenForo_RouteMatch))
#8 /index.php(13): XenForo_FrontController->run()
#9 {main}
Request State
array(3) {
  ["url"] => string(86) "https://xxx/wiki/Unicorn-extract-fictional-test?do=tags"
  ["_GET"] => array(1) {
    ["do"] => string(4) "tags"
  }
  ["_POST"] => array(6) {
    ["tags"] => string(7) "Unicorn"
    ["_xfToken"] => string(8) "********"
    ["_xfConfirm"] => string(1) "1"
    ["_xfRequestUri"] => string(50) “/wiki/Unicorn-extract-fictional-test "
    ["_xfNoRedirect"] => string(1) "1"
    ["_xfResponseType"] => string(4) "json"
  }
}