In the image_type_to_extension function the second parameter's default is '&true;' which is a string while it should be bool true. Line 950 is:

function image_type_to_extension ($imagetype, $include_dot = '&true;') {}

I believe it should be:

function image_type_to_extension ($imagetype, $include_dot = true) {}
 
As correctly stated in the functions' help:

/**
 * (PHP 5)<br/>
 * Get file extension for image type
 * @link http://php.net/manual/en/function.image-type-to-extension.php
 * @param int $imagetype <p>
 * One of the IMAGETYPE_XXX constant.
 * </p>
 * @param bool $include_dot [optional] <p>
 * Whether to prepend a dot to the extension or not. Default to <b>TRUE</b>.
 * </p>
 * @return string A string with the extension corresponding to the given image type.
 */

Regards,

Paolo