xs:choice is causing xsd assert error #16

AssertionError [ERR_ASSERTION]: { 'xsd:choice':
   [ { 'xsd:annotation':
        [ { 'xsd:documentation':
             [ '\n            Purchase\n            order schema.\n          ' ] } ],
       'xsd:choice':
        [ { '$': { minOccurs: '1', maxOccurs: '1' },
            'xsd:element':
             [ { '$': { name: 'purchaseOrder', type: 'PurchaseOrderType' } } ] } ],
       'xs:any':
        [ { '$': { namespace: '##other', processContents: 'lax' } } ] } ] }
    at assert (/Users/test-user/workspace/poc/xmltojson/node/node_modules/xml4js/lib/assert.js:10:5)
    at /Users/test-user/workspace/poc/xmltojson/node/node_modules/xml4js/lib/xsd.js:584:9
    at parseNamespacePrefixes (/Users/test-user/workspace/poc/xmltojson/node/node_modules/xml4js/lib/xsd.js:502:3)
    at /Users/test-user/workspace/poc/xmltojson/node/node_modules/xml4js/lib/xsd.js:548:7
    at Parser.<anonymous> (/Users/test-user/workspace/poc/xmltojson/node/node_modules/xml4js/node_modules/xml2js/lib/xml2js.js:492:18)
    at Parser.emit (events.js:198:13)
    at SAXParser.onclosetag (/Users/test-user/workspace/poc/xmltojson/node/node_modules/xml4js/node_modules/xml2js/lib/xml2js.js:453:26)
    at emit (/Users/test-user/workspace/poc/xmltojson/node/node_modules/sax/lib/sax.js:624:35)
    at emitNode (/Users/test-user/workspace/poc/xmltojson/node/node_modules/sax/lib/sax.js:629:5)
    at closeTag (/Users/test-user/workspace/poc/xmltojson/node/node_modules/sax/lib/sax.js:889:7)

<?xml version=\"1.0\"?><purchaseOrder orderDate=\"1999-10-20\" validDate=\"1999-10-20\" xmlns=\"http://www.example.com/PO\"><shipTo country=\"US\"><name>Alice Smith</name><street>123 Maple Street</street><city>Mill Valley</city><state>CA</state><zip>90952</zip></shipTo><billTo country=\"US\"><name>Robert Smith</name><street>8 Oak Avenue</street><city>Old Town</city><state>PA</state><zip>95819</zip></billTo><comment>Hurry, my lawn is going wild!</comment><items><item partNum=\"872-AA\"><productName>Lawnmower</productName><quantity>1</quantity><USPrice>148.95</USPrice><comment>Confirm this is electric</comment></item><item partNum=\"926-AA\"><productName>Baby Monitor</productName><quantity>1</quantity><USPrice>39.98</USPrice><shipDate>1999-05-21</shipDate></item></items></purchaseOrder>

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://www.example.com/PO" targetNamespace="http://www.example.com/PO">
  <xsd:element name='comment' type='xsd:string'/>
 <xsd:choice>
        <xsd:annotation>
          <xsd:documentation>
            Purchase
            order schema.
          </xsd:documentation>
        </xsd:annotation>
        <xsd:choice minOccurs="1" maxOccurs="1">
            <xsd:element name="purchaseOrder" type="PurchaseOrderType"/>
        </xsd:choice>
<xsd:any namespace="##other" processContents="lax" />
        </xsd:choice>
  <xsd:complexType name='USAddress'>
    <xsd:annotation>
      <xsd:documentation>
        Purchase order schema for Example.Microsoft.com.
      </xsd:documentation>
    </xsd:annotation>
    <xsd:sequence>
      <xsd:element name='name'   type='xsd:string'/>
      <xsd:element name='street' type='xsd:string'/>
      <xsd:element name='city'   type='xsd:string'/>
      <xsd:element name='state'  type='xsd:string'/>
      <xsd:element name='zip'    type='xsd:decimal'/>
    </xsd:sequence>
    <xsd:attribute name='country' type='xsd:NMTOKEN' fixed='US'/>
  </xsd:complexType>

  <xsd:simpleType name='SKU'>
    <xsd:restriction base='xsd:string'>
      <xsd:pattern value='\d{3}\w{3}'/>
    </xsd:restriction>
  </xsd:simpleType>

  <xsd:complexType name='Items'>
    <xsd:sequence>
      <xsd:element name='item' minOccurs='0' maxOccurs='unbounded'>
        <xsd:complexType>
          <xsd:sequence>
            <xsd:element name='productName' type='xsd:string'/>
            <xsd:element name='quantity'>
              <xsd:simpleType>
                <xsd:restriction base='xsd:positiveInteger'>
                  <xsd:minInclusive value='1'/>
                  <xsd:maxExclusive value='100'/>
                </xsd:restriction>
              </xsd:simpleType>
            </xsd:element>
            <xsd:element name='USPrice'  type='xsd:decimal'/>
            <xsd:element ref='comment'/>
            <xsd:element name='shipDate' type='xsd:date' minOccurs='0'/>
          </xsd:sequence>
          <xsd:attribute name='partNum' type='SKU'/>
        </xsd:complexType>
      </xsd:element>
    </xsd:sequence>
  </xsd:complexType>

  <xsd:complexType name='PurchaseOrderType'>
    <xsd:sequence>
      <xsd:element name='shipTo' type='USAddress'/>
      <xsd:element name='billTo' type='USAddress'/>
      <xsd:element ref='comment' minOccurs='0'/>
      <xsd:element name='items'  type='Items'/>
    </xsd:sequence>

    <xsd:attribute name="validDate" type="xsd:date"/>
    <xsd:attribute name='orderDate' type='xsd:date'/>
    <xsd:attribute name='confirmDate' type='xsd:date' use='required'/>
  </xsd:complexType>
</xsd:schema>