Error thrown when running existing Laravel project on local server - laravel

Question

UPDATE: I think updating to a newer php version (by updating homebrew) causes this problem... Could/should I update the Laravel version of the project I'm working on? Or install a lower php version? I have no experience with that...
I'm working on a Laravel project for quite some time no. All of a sudden an exception is thrown when starting the local server.
The ErrorException is: trim(): Passing null to parameter #1 ($string) of type string is deprecated
It points to a few lines in the routes/web.php file.
ErrorException
trim(): Passing null to parameter #1 ($string) of type string is deprecated
at vendor/laravel/framework/src/Illuminate/Routing/RouteGroup.php:65
61▕ {
62▕ $old = $old['prefix'] ?? null;
63▕
64▕ if ($prependExistingPrefix) {
➜ 65▕ return isset($new['prefix']) ? trim($old, '/').'/'.trim($new['prefix'], '/') : $old;
66▕ } else {
67▕ return isset($new['prefix']) ? trim($new['prefix'], '/').'/'.trim($old, '/') : $old;
68▕ }
69▕ }
+6 vendor frames
7 routes/web.php:90
Illuminate\Routing\RouteRegistrar::group(Object(Closure))
+3 vendor frames
11 routes/web.php:91
Illuminate\Routing\RouteRegistrar::group(Object(Closure))
This are the lines in the web.php file
Route::middleware(['auth.isAdminPers'])->group(function () {
Route::get('/admin/admin',function () {
return view('admin.admin');
});
Route::get('admin/dienstverplaatsingen',[AdminDienstverplaatsingController::class,'index'])->name('admin.dienstverplaatsingen');
Route::get('/admin/experiment',[gebruikerController::class, 'experiment']);
Route::get('/admin/export',[AdminDienstverplaatsingController::class,'export']);
Route::get('/admin/fietsritten', [AdminFietsritten::class,'index'])->name('admin.fietsritten');
Route::get('/admin/fietsrittengrouped', [fietsrittengrouped::class, 'index'])->name('admin.fietsrittengrouped');
Route::get('/admin/maaltijden',[AdminMaaltijden::class,'index'])->name('admin.maaltijden');
Route::get('/admin/maaltijdengrouped',[maaltijdengrouped::class,'index'])->name('admin.maaltijdengrouped');
Route::prefix('admin')->name('admin.')->group(function(){
Route::get('/users/export', [UserController::class,'export'])->name('users.export');
Route::resource('/users', UserController::class);
Route::get('/appsettings', function(){
return view('admin.settings');
})->name('appsettings');
});
});

Answer 1

I just had this problem earlier. The way I have solved it was by running php artisan route:cache before composer install. Keep in mind that I am using PHP 7.4 with Laravel 8.