1you haven't initialized the variable $user so in the controller and before using it you've to add $user = new User; assuming that you already have use App\User;
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3or $user = new \App\User; if you don't.
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5Update if you're trying to update an existing user record you've to initialize the $user variable by selecting based on it's primary key which should be sent in the request and then doing the initialization like:
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7$user_id = $request->input('user_id');
8$user = User::find($user_id);