bbp_get_topic_author_avatar( int $topic_id, int $size = 40 )

	function bbp_get_topic_author_avatar( $topic_id = 0, $size = 40 ) {
		$author_avatar = '';

		$topic_id = bbp_get_topic_id( $topic_id );
		if ( !empty( $topic_id ) ) {
			if ( !bbp_is_topic_anonymous( $topic_id ) ) {
				$author_avatar = get_avatar( bbp_get_topic_author_id( $topic_id ), $size );
			} else {
				$author_avatar = get_avatar( get_post_meta( $topic_id, '_bbp_anonymous_email', true ), $size );
			}
		}

		return apply_filters( 'bbp_get_topic_author_avatar', $author_avatar, $topic_id, $size );
	}