Description:
------------
First, My main concern is FALSE and NULL values not filter function array_filter.

Second, There should be more parameter for array_filter for string and integer type.

Test script:
---------------
$tag_string = 'logo,sky,bird,-0,fire,-1,0,2333,false,logo,FALSE,null,COMPANY,Fire,NULL';

$tag_arr = explode(',', $tag_string );

$tag_arr = array_filter($tag_arr);

print_r($tag_arr);

Expected result:
----------------
Array
(
    [0] => logo
    [1] => sky
    [2] => bird
    [3] => fire
    [4] => 2333
    [5] => logo
    [6] => COMPANY
    [7] => Fire
)

Actual result:
--------------
Array
(
    [0] => logo
    [1] => sky
    [2] => bird
    [3] => -0
    [4] => fire
    [5] => -1
    [7] => 2333
    [8] => false
    [9] => logo
    [10] => FALSE
    [11] => null
    [12] => COMPANY
    [13] => Fire
    [14] => NULL
)