Ship middleware to trim strings and convert empty strings to null.

src/Illuminate/Foundation/Http/Middleware/ConvertEmptyStringsToNull.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace Illuminate\Foundation\Http\Middleware;
+
+class ConvertEmptyStringsToNull extends TransformsRequest
+{
+    /**
+     * Transform the given value.
+     *
+     * @param  string  $key
+     * @param  mixed  $value
+     * @return mixed
+     */
+    protected function transform($key, $value)
+    {
+        return is_string($value) && $value === '' ? null : $value;
+    }
+}

src/Illuminate/Foundation/Http/Middleware/TransformsRequest.php

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+<?php
+
+namespace Illuminate\Foundation\Http\Middleware;
+
+use Closure;
+use Symfony\Component\HttpFoundation\ParameterBag;
+
+class TransformsRequest
+{
+    /**
+     * The additional attributes passed to the middleware.
+     *
+     * @var array
+     */
+    protected $attributes = [];
+
+    /**
+     * Handle an incoming request.
+     *
+     * @param  \Illuminate\Http\Request  $request
+     * @param  \Closure  $next
+     * @return mixed
+     */
+    public function handle($request, Closure $next, ...$attributes)
+    {
+        $this->attributes = $attributes;
+
+        $this->clean($request);
+
+        return $next($request);
+    }
+
+    /**
+     * Clean the request's data.
+     *
+     * @param  \Illuminate\Http\Request  $request
+     * @return void
+     */
+    protected function clean($request)
+    {
+        $this->cleanParameterBag($request->query);
+
+        $this->cleanParameterBag($request->request);
+
+        if ($request->isJson()) {
+            $this->cleanParameterBag($request->json());
+        }
+    }
+
+    /**
+     * Clean the data in the parameter bag.
+     *
+     * @param  \Symfony\Component\HttpFoundation\ParameterBag  $bag
+     * @return void
+     */
+    protected function cleanParameterBag(ParameterBag $bag)
+    {
+        $bag->replace($this->cleanArray($bag->all()));
+    }
+
+    /**
+     * Clean the data in the given array.
+     *
+     * @param  array  $data
+     * @return array
+     */
+    protected function cleanArray(array $data)
+    {
+        return collect($data)->map(function ($value, $key) {
+            return $this->cleanValue($key, $value);
+        })->all();
+    }
+
+    /**
+     * Clean the given value.
+     *
+     * @param  string  $key
+     * @param  mixed  $value
+     * @return mixed
+     */
+    protected function cleanValue($key, $value)
+    {
+        if (is_array($value)) {
+            return $this->cleanArray($value);
+        }
+
+        return $this->transform($key, $value);
+    }
+
+    /**
+     * Transform the given value.
+     *
+     * @param  string  $key
+     * @param  mixed  $value
+     * @return mixed
+     */
+    protected function transform($key, $value)
+    {
+        return $value;
+    }
+}

src/Illuminate/Foundation/Http/Middleware/TrimStrings.php

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+<?php
+
+namespace Illuminate\Foundation\Http\Middleware;
+
+class TrimStrings extends TransformsRequest
+{
+    /**
+     * The attributes that should not be trimmed.
+     *
+     * @var array
+     */
+    protected $except = [
+        //
+    ];
+
+    /**
+     * Transform the given value.
+     *
+     * @param  string  $key
+     * @param  mixed  $value
+     * @return mixed
+     */
+    protected function transform($key, $value)
+    {
+        if (in_array($key, $this->except)) {
+            return $value;
+        }
+
+        return is_string($value) ? trim($value) : $value;
+    }
+}