Description:
------------
* This is different than bug http://bugs.php.net/bug.php?id=41305 *

The filter_var() vs. the filter_input() behave differently when using the 
FILTER_VALIDATE_BOOLEAN filter when the variable/input doesn't exist.

More specifically, it seems as if the FILTER_NULL_ON_FAILURE flag is set 
automatically in the filter_input() function.

(Note: same behavior for filter_var_array() vs. filter_input_array()).

From PHPINFO():
filter.default = unsafe_raw
filter.default_flags = no value
Revision: 1.52.2.39.2.16

Test script:
---------------
<?php
// example.com/script.php?arg1=yes&arg3=no

// filtering by variable
$var1 = filter_var($_GET["arg1"], FILTER_VALIDATE_BOOLEAN);
$var2 = filter_var($_GET["arg2"], FILTER_VALIDATE_BOOLEAN);
$var3 = filter_var($_GET["arg3"], FILTER_VALIDATE_BOOLEAN);

// filtering by input
$input1 = filter_input(INPUT_GET, "arg1", FILTER_VALIDATE_BOOLEAN);
$input2 = filter_input(INPUT_GET, "arg2", FILTER_VALIDATE_BOOLEAN);
$input3 = filter_input(INPUT_GET, "arg3", FILTER_VALIDATE_BOOLEAN);

// as expected...
var_dump($var1);      // bool(true)
var_dump($var2);      // bool(false)
var_dump($var3);      // bool(false)

// NULL is not an expected return unless the FILTER_NULL_ON_FAILURE flag is set...
var_dump($input1);    // bool(true)
var_dump($input2);    // NULL
var_dump($input3);    // bool(false)
?>

Expected result:
----------------
As per the documentation, we expect the output of the code above to be:

bool(true)
bool(false)
bool(false)
bool(true)
bool(false)
bool(false)

Actual result:
--------------
Even though the FILTER_NULL_ON_FAILURE flag is NOT set, we DO get a NULL value in 
the output:

bool(true)
bool(false)
bool(false)
bool(true)
NULL
bool(false)