Adding custom Team Profile fields

Hi there, I've been trying to add URL field to Teams Profile Page that will allow team members to manually create their team URL in order to let public visitors see the team's portfolio. (e.g. http://www.webapp.com/{URL}) I've followed the instructions "Adding Profile Fields" given on the Spark documentation. Since the documentation is about the User Profile, I'm stuck when I apply it for Team Profile.

I've done the migration, update the views and controllers so far. The validations on the controller are working and the data -I manually entered URL to the database- appears in the form field. However when I click on the update button on the profile page, it gives "500 Internal Server Error" on the developer console. Do you have any idea why it denies to record on MySQL database?

Include update-team-url Blade in to /resources/views/vendor/spark/settings/teams/team-profile.blade.php

<spark-team-profile :user="user" :team="team" inline-template>
    <div>
        <div v-if="user && team">
            <!-- Update Team Photo -->
            @include('spark::settings.teams.update-team-photo')

            <!-- Update Team Name -->
            @include('spark::settings.teams.update-team-name')
            
            <!-- Update Team URL-->
            @include('spark::settings.teams.update-team-url')
        </div>
    </div>
</spark-team-profile>

Then create the update-team-url.blade.php

<spark-update-team-url :user="user" :team="team" inline-template>
    <div class="panel panel-default">
        <div class="panel-heading">Update Event URL</div>

        <div class="panel-body">
            <!-- Success Message -->
            <div class="alert alert-success" v-if="form.successful">
                Your event URL has been updated!
            </div>

            <form class="form-horizontal" role="form">
                <!-- URL -->
                <div class="form-group" :class="{'has-error': form.errors.has('url')}">
                    <label class="col-md-4 control-label">URL</label>

                    <div class="col-md-6">
                        <input type="text" class="form-control" name="url" v-model="form.url">

                        <span class="help-block" v-show="form.errors.has('url')">
                            @{{ form.errors.get('url') }}
                        </span>
                    </div>
                </div>

                <!-- Update Button -->
                <div class="form-group">
                    <div class="col-md-offset-4 col-md-6">
                        <button type="submit" class="btn btn-primary"
                                @click.prevent="update"
                                :disabled="form.busy">

                            Update
                        </button>
                    </div>
                </div>
            </form>
        </div>
    </div>
</spark-update-team-url>

Define the Vue component:

Vue.component('spark-update-team-url', {
    props: ['user', 'team'],
    
    /**
     * The component's data.
     */
    data() {
        return {
            form: new SparkForm({
                url: ''
            })
        };
    },

    /**
     * Prepare the component.
     */
    ready() {
        this.form.url = this.team.url;
    },
    
     methods: {
        /**
         * Update the team url.
         */
        update() {
            Spark.put(`/settings/teams/${this.team.id}/url`, this.form)
                .then(() => {
                    this.$dispatch('updateTeam');
                    this.$dispatch('updateTeams');
                });
        }
    }
});

Route file:

Route::put('/settings/teams/{team}/url', 'Settings\Teams\TeamUrlController@update');

Controller:

<?php

namespace App\Http\Controllers\Settings\Teams;

use Illuminate\Http\Request;
use App\Http\Controllers\Controller;

class TeamUrlController extends Controller
{
    /**
     * Create a new controller instance.
     *
     * @return void
     */
    public function __construct()
    {
        $this->middleware('auth');
    }

    /**
     * Update the given team's URL.
     *
     * @param  Request  $request
     * @param  \Laravel\Spark\Team  $team
     * @return Response
     */
    public function update(Request $request, $team)
    {
        abort_unless($request->user()->ownsTeam($team), 404);

        $this->validate($request, [
            'url' => 'required|min:3|alpha_dash|unique',
        ]);

        $team->forceFill([
            'url' => $request->url,
        ])->save();
        
    }
}

And the migration:

public function up()
    {
        Schema::table('teams', function (Blueprint $table) {
            $table->string('url');
        });
    }

Screenshots:

Thanks.