PHP 7.4 - Trying to access array offset on value of type null

After update to php 7.4, sometimes get this error:

Trying to access array offset on value of type null {"exception":"[object] (ErrorException(code: 0): Trying to access array offset on value of type null at /vendor/mobiledetect/mobiledetectlib/Mobile_Detect.php:1056)
[stacktrace]
#0 /vendor/mobiledetect/mobiledetectlib/Mobile_Detect.php(1056): Illuminate\\Foundation\\Bootstrap\\HandleExceptions->handleError(8, 'Trying to acces...', '/var/www/konkur...', 1056, Array)
#1 /vendor/mobiledetect/mobiledetectlib/Mobile_Detect.php(1177): Mobile_Detect->checkHttpHeadersForMobile()
#2 /vendor/jenssegers/agent/src/Agent.php(266): Mobile_Detect->isMobile(NULL, NULL)
#3 /vendor/laravel/framework/src/Illuminate/Support/Facades/Facade.php(239): Jenssegers\\Agent\\Agent->isDesktop()
#4 /app/Http/Middleware/MobileDetect.php(28): Illuminate\\Support\\Facades\\Facade::__callStatic('isDesktop', Array)
#5 /vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(163): App\\Http\\Middleware\\MobileDetect->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#6 /vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#7 /vendor/laravel/framework/src/Illuminate/Foundation/Http/Middleware/TransformsRequest.php(21): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#8 /vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(163): Illuminate\\Foundation\\Http\\Middleware\\TransformsRequest->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#9 /vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#10 /vendor/laravel/framework/src/Illuminate/Foundation/Http/Middleware/ValidatePostSize.php(27): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#11 /vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(163): Illuminate\\Foundation\\Http\\Middleware\\ValidatePostSize->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#12 /vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#13 /vendor/laravel/framework/src/Illuminate/Foundation/Http/Middleware/CheckForMaintenanceMode.php(62): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#14 /vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(163): Illuminate\\Foundation\\Http\\Middleware\\CheckForMaintenanceMode->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#15 /vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#16 /vendor/fideloper/proxy/src/TrustProxies.php(57): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#17 /vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(163): Fideloper\\Proxy\\TrustProxies->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#18 /vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#19 /vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(104): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#20 /vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(151): Illuminate\\Pipeline\\Pipeline->then(Object(Closure))
#21 /vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(116): Illuminate\\Foundation\\Http\\Kernel->sendRequestThroughRouter(Object(Illuminate\\Http\\Request))
#22 /public/index.php(55): Illuminate\\Foundation\\Http\\Kernel->handle(Object(Illuminate\\Http\\Request))
#23 {main}
"}

$matchType['matches'] isn't set

Start at vendor/mobiledetect/mobiledetectlib/Mobile_Detect.php:1056 in checkHttpHeadersForMobile(), then follow the call from isMobile() shown at line 1177. Reproduce the PHP 7.4 warning and verify that requests reaching this path no longer try to access an unset matches offset.

Written by the indexing model from the issue text.