title: Laravel 5.4 UnexpectedValueException in Response.php line 444 in form submition
body: <p>I am making multiauth. When I submit admin email and password from admin login view I got bellow error 
  "UnexpectedValueException in Response.php line 444:
  The Response content must be a string or object implementing __toString(), "boolean" given."
  here is my form</p>
  
  <pre><code>@extends('layouts.app')
  
  @section('content')
      &lt;div class="container"&gt;
          &lt;div class="row"&gt;
              &lt;div class="col-md-8 col-md-offset-2"&gt;
                  &lt;div class="panel panel-default"&gt;
                      &lt;div class="panel-heading"&gt;Admin Login&lt;/div&gt;
                      &lt;div class="panel-body"&gt;
                          &lt;form class="form-horizontal" role="form" method="POST" action="{{ route('admin.login.submit') }}"&gt;
                              {{ csrf_field() }}
  
                              &lt;div class="form-group{{ $errors-&gt;has('email') ? ' has-error' : '' }}"&gt;
                                  &lt;label for="email" class="col-md-4 control-label"&gt;E-Mail Address&lt;/label&gt;
  
                                  &lt;div class="col-md-6"&gt;
                                      &lt;input id="email" type="email" class="form-control" name="email" value="{{ old('email') }}" required autofocus&gt;
  
                                      @if ($errors-&gt;has('email'))
                                          &lt;span class="help-block"&gt;
                                          &lt;strong&gt;{{ $errors-&gt;first('email') }}&lt;/strong&gt;
                                      &lt;/span&gt;
                                      @endif
                                  &lt;/div&gt;
                              &lt;/div&gt;
  
                              &lt;div class="form-group{{ $errors-&gt;has('password') ? ' has-error' : '' }}"&gt;
                                  &lt;label for="password" class="col-md-4 control-label"&gt;Password&lt;/label&gt;
  
                                  &lt;div class="col-md-6"&gt;
                                      &lt;input id="password" type="password" class="form-control" name="password" required&gt;
  
                                      @if ($errors-&gt;has('password'))
                                          &lt;span class="help-block"&gt;
                                          &lt;strong&gt;{{ $errors-&gt;first('password') }}&lt;/strong&gt;
                                      &lt;/span&gt;
                                      @endif
                                  &lt;/div&gt;
                              &lt;/div&gt;
  
                              &lt;div class="form-group"&gt;
                                  &lt;div class="col-md-6 col-md-offset-4"&gt;
                                      &lt;div class="checkbox"&gt;
                                          &lt;label&gt;
                                              &lt;input type="checkbox" name="remember" {{ old('remember') ? 'checked' : '' }}&gt; Remember Me
                                          &lt;/label&gt;
                                      &lt;/div&gt;
                                  &lt;/div&gt;
                              &lt;/div&gt;
  
                              &lt;div class="form-group"&gt;
                                  &lt;div class="col-md-8 col-md-offset-4"&gt;
                                      &lt;button type="submit" class="btn btn-primary"&gt;
                                          Login
                                      &lt;/button&gt;
  
                                      &lt;a class="btn btn-link" href="{{ route('password.request') }}"&gt;
                                          Forgot Your Password?
                                      &lt;/a&gt;
                                  &lt;/div&gt;
                              &lt;/div&gt;
                          &lt;/form&gt;
                      &lt;/div&gt;
                  &lt;/div&gt;
              &lt;/div&gt;
          &lt;/div&gt;
      &lt;/div&gt;
  @endsection
  </code></pre>
  
  <p>And here is route</p>
  
  <pre><code>Route::prefix('admin')-&gt;group(function (){
      Route::post('/login', 'Auth\AdminLoginController@login')-&gt;name('admin.login.submit');
  });
  </code></pre>
  
  <p>And the controller is here</p>
  
  <pre><code>&lt;?php
  
  namespace App\Http\Controllers\Auth;
  
  use Illuminate\Http\Request;
  use App\Http\Controllers\Controller;
  
  class AdminLoginController extends Controller
  {
      public function __construct()
      {
          $this-&gt;middleware('guest');
      }
  
      public function showLoginForm()
      {
          return view('admin.auth.login');
      }
      public function login(Request $request)
      {
          return true;
      }
  }
  </code></pre>
  
  <p>What wrong here?
  And How can I solve it?</p>
  
  <p>Thanks in advance.</p>