BuddyPress.org

Hy, I have a Problem.
In the Widget i have this code, becouse see Only the Avatar from gravatar.com and not from Buddypress or WordPress

<?php echo get_avatar( $comment, '45' ); ?>
Display in Html
<img alt="" src="https://secure.gravatar.com/avatar/ca07c51aecfa704741559ccc813d7b0d?s=45&d=mm&r=g" srcset="https://secure.gravatar.com/avatar/ca07c51aecfa704741559ccc813d7b0d?s=90&d=mm&r=g 2x" class="avatar avatar-45 gravatar" height="45" width="45">

Than i have change the code to:
<?php echo bp_core_fetch_avatar( array( 'item_id' => $comment->user_id,'type' => 'full','width' => 75,'height' => 75)); ?>
becouse is not working.

What is the correct code for Display Avatar from a Comment.

Thanks a lot