Description:
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When testing arrays for a key's existance with isset() or empty(), a float key is treated as zero in PHP v5. This behavior differs from PHP v4.3.6.

Reproduce code:
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$MyArray[0] = 'zero';
$key = (float) 5;
$isset = isset($MyArray[$key]);
var_dump($isset);

Expected result:
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bool(false)

Actual result:
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bool(true)