Source

File: wp-admin/includes/class-wp-ms-users-list-table.php

public function column_name( $user ) {
		if ( $user->first_name && $user->last_name ) {
			echo "$user->first_name $user->last_name";
		} elseif ( $user->first_name ) {
			echo $user->first_name;
		} elseif ( $user->last_name ) {
			echo $user->last_name;
		} else {
			echo '<span aria-hidden="true">&#8212;</span><span class="screen-reader-text">' . _x( 'Unknown', 'name' ) . '</span>';
		}
	}