Illegal String Offset 'class' in PHP - php

Question

I received this warning
Warning: Illegal string offset 'class' in C:\xampp\htdocs\myweb\libraries\cms\html\html.php on line 971
Warning: Illegal string offset 'class' in C:\xampp\htdocs\myweb\libraries\cms\html\html.php on line 972
Warning: Illegal string offset 'class' in C:\xampp\htdocs\myweb\libraries\cms\html\html.php on line 972
On joomla 3.3 (file path \libraries\cms\html\html.php) and the code is:
public static function calendar($value, $name, $id, $format = '%Y-%m-%d', $attribs = null)
{
static $done;
if ($done === null)
{
$done = array();
}
$attribs['class'] = isset($attribs['class']) ? $attribs['class'] : 'input-medium';//happen here
$attribs['class'] = trim($attribs['class'] . ' hasTooltip');//happen here
$readonly = isset($attribs['readonly']) && $attribs['readonly'] == 'readonly';
$disabled = isset($attribs['disabled']) && $attribs['disabled'] == 'disabled';
if (is_array($attribs))
{
$attribs = JArrayHelper::toString($attribs);
}
.......
Shows that it had to do with $attribs['class']. And if I'm correct illegal string offset could mean that $attribs is not an array but a string. So is there any way to correct this?
I'm on PHP5.4

Answer 1

This:
public static function calendar($value, $name, $id, $format = '%Y-%m-%d', $attribs = null)
{
}
Should be:
public static function calendar($value, $name, $id, $format = '%Y-%m-%d', $attribs = array())
{
}
Point is that by setting "null" to the variable by default, you actually say it's an empty string, or an empty variable. By setting "array()", you define the variable being an empty array.
Just by looking a little bit further, there is an array expected, since the code is looking for specific array_keys like: 'readonly' AND 'disabled'.