How to handle missing nodes when producing flat XML

Question

Hi All, I have XSLT to transform the complex XML to flat XML as per shown below. How can I fine tuning the XSLT coding below to ensure handle the missing nodes. Currently, for example below, the payment info nodes is missing for the OrderID=1. However, after I run XSLT the entire information for OrderID=1 is missing after transform. How can I get the expected output expected_ouput_flat_oder_xml.xml from the sample source order Order_xml.xml?

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
   <!-- Define the output method as XML and indent the output --> 
    <xsl:output method="xml" indent="yes"/>
  
   <!-- Template matching the root element /Orders -->
    <xsl:template match="/Orders">
        <Orders>
            <xsl:apply-templates select="Order"/> <!-- Apply templates to all Order elements -->
        </Orders>
    </xsl:template>
  <!-- Template matching Order elements -->
    <xsl:template match="Order">
        <xsl:variable name="o" select="."/>  <!-- Variable to hold the current Order node -->
    <!-- Loop through OrderDetails/Detail/ShippedRemarks elements -->
                <xsl:for-each select="$o/OrderDetails/Detail/ShippedRemarks"> <!-- Check if $o/OrderDetails/Detail/ShippedRemarks exists -->
                    <xsl:variable name="shr" select="."/>  <!-- Variable to hold the current ShippedRemarks node -->
                    <xsl:variable name="d" select=".."/>   <!-- Variable to hold the parent Detail node -->
     
	 <!-- Loop through ProductDetails/DetailName elements -->
                <xsl:for-each select="$o/ProductDetails/DetailName">
                    <xsl:variable name="dn" select="."/>  <!-- Variable to hold the current DetailName node -->
				
		<!-- Loop through PaymentInfo elements -->
	            <xsl:for-each select="$o/PaymentInfo">
					<xsl:variable name="pi" select="."/> <!-- Variable to hold the current PaymentInfo node -->	
          
		    <!-- Output an Order element with the combined data -->
                <Order>
                    <xsl:copy-of select="$o/OrderID | $o/CustomerID | $o/OrderDate"/> <!-- Copy values from the Order node -->
                    <xsl:copy-of select="$d/ProductID | $d/Quantity"/> <!-- Copy values from the parent DetailName node -->
                    <xsl:copy-of select="$shr/*"/>  <!-- Copy values from the parent ShippedRemarks node -->
                    <xsl:copy-of select="$dn/*"/> <!-- Copy values from the current DetailName node -->
                    <xsl:copy-of select="$pi/*"/> <!-- Copy values from the current PaymentInfo node -->
                </Order>
                
				   </xsl:for-each>
            </xsl:for-each>
        </xsl:for-each>
    </xsl:template>
</xsl:stylesheet>