How to avoid undefined offset

list($func, $field) = array_pad(explode('|', $value, 2), 2, null);

Two changes:

• It limits the size of the array returned by explode() to 2. It seems, that no more than this is wanted
• If there are fewer than two values returned, it appends null until the array contains 2 values. See Manual: array_pad() for further information

This means, if there is no | in $value, $field === null. Of course you can use every value you like to define as default for $field (instead of null). Its also possible to swap the behavior of $func and $field

list($func, $field) = array_pad(explode('|', $value, 2), -2, null);

Now $func is null, when there is no | in $value.