Index: wp-admin/includes/class-wp-ms-users-list-table.php
===================================================================
--- wp-admin/includes/class-wp-ms-users-list-table.php	(revision 40900)
+++ wp-admin/includes/class-wp-ms-users-list-table.php	(working copy)
@@ -258,7 +258,11 @@
 	 * @param WP_User $user The current WP_User object.
 	 */
 	public function column_name( $user ) {
-		echo "$user->first_name $user->last_name";
+		if ( ! empty( $user->first_name ) || ! empty( $user->last_name ) ) {
+		 	echo "$user->first_name $user->last_name";
+	 	} else {
+			echo _x( 'Unknown' );
+	 	}
 	}
 
 	/**
Index: wp-admin/includes/class-wp-users-list-table.php
===================================================================
--- wp-admin/includes/class-wp-users-list-table.php	(revision 40900)
+++ wp-admin/includes/class-wp-users-list-table.php	(working copy)
@@ -471,7 +471,11 @@
 						$r .= "$avatar $edit";
 						break;
 					case 'name':
-						$r .= "$user_object->first_name $user_object->last_name";
+						if ( ! empty( $user_object->first_name ) || ! empty( $user_object->last_name ) ) {
+						 	$r .= "$user_object->first_name $user_object->last_name";
+					 	} else {
+							$r .= _x( 'Unknown' );
+					 	}
 						break;
 					case 'email':
 						$r .= "<a href='" . esc_url( "mailto:$email" ) . "'>$email</a>";