Add new column to WooCommerce Orders page

woocommerce-add-new-column-on-orders-page.php

<?php 

add_filter( 'manage_edit-shop_order_columns', 'MY_COLUMNS_FUNCTION' );
function MY_COLUMNS_FUNCTION( $columns ) {
	$new_columns = ( is_array( $columns ) ) ? $columns : array();
  	unset( $new_columns[ 'order_actions' ] );
	
  	//edit this for your column(s)
  	//all of your columns will be added before the actions column
  	$new_columns['MY_COLUMN_ID_1'] = 'MY_COLUMN_1_TITLE';
  	$new_columns['MY_COLUMN_ID_2'] = 'MY_COLUMN_2_TITLE';
	
  	//stop editing
  	$new_columns[ 'order_actions' ] = $columns[ 'order_actions' ];
  	return $new_columns;
}

Throws error now: "PHP Notice: Undefined index: order_actions" in version 3.7.0.