countBy method fails if the field name is passed as a string

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• Laravel Version: 7.25.0
• PHP Version: 7.2.33
• Database Driver & Version: mysql & 8.0.21

Description:

With respect to the commit #33801
Returns error "Called to undefined function " on countBy method if the field name is passed as a string.

Steps To Reproduce:

Laravel version 7.24.0

$collection = collect([
    ['type' => 'O+', 'name' => 'John'],
    ['type' => 'O-', 'name' => 'Joe'],
    ['type' => 'O+', 'name' => 'Justin']
]);

$collection->countBy('type');

// returns
Illuminate\Support\Collection {#4859
    all: [
        "O+" => 2,
        "O-" => 1,
    ],
}

Laravel version 7.25.0

$collection = collect([
    ['type' => 'O+', 'name' => 'John'],
    ['type' => 'O-', 'name' => 'Joe'],
    ['type' => 'O+', 'name' => 'Justin']
]);

$collection->countBy('type');

// returns
Call to undefined function type() in vendor/laravel/framework/src/Illuminate/Support/LazyCollection.php on line 259

[driesvints]

Ping @JosephSilber

[JosephSilber]

Sorry for breaking that 😢

There was no test covering this. I submitted a PR with a fix that also includes the obligatory tests.

[driesvints]

Thanks @JosephSilber.