Description:
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If the same member variable is returned twice from __sleep() and that member variable is a reference, the serialized output errors when unserialized.  This "worked" before PHP7 and the error during unserialization appears in PHP 7.0.3 and later.  

Test script:
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<?php

class C { }
class A { public $b; function __construct() { $this->b = new C(); }  function __sleep() {  return array("b", "b"); } }
$a = new A();
var_dump(unserialize(serialize($a)));

Expected result:
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Notice: member variable "b" returned from __sleep() multiple times
or alternately, silently ignore the duplication.


Actual result:
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Notice: unserialize(): Error at offset 43 of 44 bytes in /in/0FNkge on line 6
bool(false)