Description:
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array_search($value,$arr);

the returns of this function is not expected。it displays false or the key from doc. but I get false、null、key。

php -version : 5.6.10

Test script:
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$arr = null;
$key = array_search(2, $arr);
if( $key === false)
   echo 'no value';
else
   echo 'the key is '.$key;