Pass by reference error in Theme settings

line 649, illegal parameter passing (the 1st param)

file_check_directory(variable_get('file_directory_path', 'files'), FILE_CREATE_DIRECTORY, 'file_directory_path');

it should look like this

$directory_path = variable_get('file_directory_path', 'files');
file_check_directory($directory_path, FILE_CREATE_DIRECTORY, 'file_directory_path');