Statamic on an existing Laravel app produces error at login get_class(): Argument #1 ($object) must be of type object, null given

[riordanmb]

I have followed the steps here, here and here, to install on an existing Laravel app alongside the Nova control panel. My first error was a permissions issue, which I have resolved. But I am now seeing this error:

get_class(): Argument #1 ($object) must be of type object, null

when I attempt to login at https://mywebite.com/cp using my email and password stored in the 'users' table. The stack trace suggests an error at UserRepository.php at line 55: return call_user_func_array([$model, $method], $args); and 44:

public function findByEmail(string $email): ?UserContract
    {
        if (! $model = $this->model('where', 'email', $email)->first()) {
            return null;
        }

I have checked my User model, which seems correct:

<?php

namespace App\Models;

use Illuminate\Foundation\Auth\User as Authenticatable;
use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Notifications\Notifiable;
use Laravel\Sanctum\HasApiTokens;

class User extends Authenticatable
{
    use HasApiTokens, HasFactory, Notifiable;

    /**
     * The attributes that are mass assignable.
     *
     * @var array<int, string>
     */
    protected $fillable = [
        'name',
        'email',
        'password',
    ];

    /**
     * The attributes that should be hidden for serialization.
     *
     * @var array<int, string>
     */
    protected $hidden = [
        'password',
        'remember_token',
    ];

    /**
     * The attributes that should be cast.
     *
     * @var array<string, string>
     */
    protected $casts = [
        'email_verified_at' => 'datetime',
    ];

    /**
     * Find a user by email.
     *
     * @param string $email
     * @return self|null
     */
    public static function findByEmail($email)
    {
        return self::where('email', $email)->first();
    }
}

Trying to log the method:

public function model($method, ...$args)
    {
        $model = $this->config['model'];
        \Log::info('Method being called: ' . $method);
        \Log::info('Model class: ' . get_class($model));
        return call_user_func_array([$model, $method], $args);
    }

gets an error:

get_class(): Argument #1 ($object) must be of type object, null given {"exception":"[object] (TypeError(code: 0): get_class(): Argument #1 ($object) must be of type object, null given at ...../vendor/statamic/cms/src/Auth/Eloquent/UserRepository.php:55)