Whether URL and Title entity properties are required is incorrectly determined

I ran into this issue when trying to set a Link field to null. I could correctly set it with:
$wrapper->{$link_field}->set(array('url' => NULL));
or
$wrapper->{$link_field}->set(NULL);
But I could not set it with
$wrapper->{$link_field}->url->set(NULL);

When I dug into the code, I saw the reason for this. The link_field_property_info_callback() function was only considering URL and Title's individual requirement rather also including the field's requirement.