Description:
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A json encoded/decoded array is converted back to an array and array_key_exists cannot find the key.

Test script:
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	$arry = [100 => 'Fe', 200 => 'Fi', 300 => 'Fo', 400 => 'Fum'];

	print(array_key_exists(100, $arry) ? '-FOUND' : '-LOST');
	print "\n";

	$obj = json_decode(json_encode($arry));

	print_r($obj);
	print_r((array)$obj);

	print(array_key_exists(100, (array)$obj) ? '-FOUND' : '-LOST');
	print "\n";