Problematic behavior when combining validation with XML catalog file

ADDITIONAL SYSTEM INFORMATION :
openjdk version "15" 2020-09-15
OpenJDK Runtime Environment (build 15+36-1562)
OpenJDK 64-Bit Server VM (build 15+36-1562, mixed mode, sharing)

A DESCRIPTION OF THE PROBLEM :
The method java.xml/javax.xml.catalog.CatalogResolverImpl.resolveEntity checks if systemId is null and if so reports the problem "JAXP09020006: The argument 'systemId' can not be null.". The thing is that when using a catalog file the systemId parameter is always set to null and this in turn triggers JAXP09020006. However if a wrapper class is introduced that implement the CatalogResolver interface and intercepts any systemId null values (replacing them with the empty string "") validation in combination with a catalog file magically start to work as expected.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Use a catalog file in combination with validation.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Validation should be able to work together with a catalog file.
ACTUAL -
(Source code for foo/Foo.java provided in the test case)

java.lang.NullPointerException: JAXP09020006: The argument 'systemId' can not be null.
        at java.xml/javax.xml.catalog.CatalogMessages.reportNPEOnNull(CatalogMessages.java:129)
        at java.xml/javax.xml.catalog.CatalogResolverImpl.resolveEntity(CatalogResolverImpl.java:70)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLEntityManager.resolveEntity(XMLEntityManager.java:1154)
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.XMLSchemaLoader.resolveDocument(XMLSchemaLoader.java:662)
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.XMLSchemaValidator.findSchemaGrammar(XMLSchemaValidator.java:2694)
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.XMLSchemaValidator.handleStartElement(XMLSchemaValidator.java:2069)
        at java.xml/com.sun.org.apache.xerces.internal.impl.xs.XMLSchemaValidator.startElement(XMLSchemaValidator.java:829)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.scanStartElement(XMLNSDocumentScannerImpl.java:374)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl$NSContentDriver.scanRootElementHook(XMLNSDocumentScannerImpl.java:613)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:3078)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:836)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:605)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:112)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:541)
        at java.xml/com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:888)
        at java.xml/com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:824)
        at java.xml/com.sun.org.apache.xerces.internal.jaxp.validation.StreamValidatorHelper.validate(StreamValidatorHelper.java:176)
        at java.xml/com.sun.org.apache.xerces.internal.jaxp.validation.ValidatorImpl.validate(ValidatorImpl.java:115)
        at foo.Foo.main(Foo.java:45)

---------- BEGIN SOURCE ----------
package foo;

import java.io.File;
import java.io.StringWriter;

import java.net.URL;
import java.net.URI;
import java.net.URISyntaxException;

import javax.xml.XMLConstants;
import javax.xml.catalog.CatalogFeatures;
import javax.xml.transform.stream.StreamSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Schema;
import javax.xml.validation.Validator;

public class Foo
{
  public static void main(String[] args)
  {
    final String catalogFile = CatalogFeatures.Feature.FILES.getPropertyName();
    final String catalogPath = "foo/catalog.xml";

    final ClassLoader classLoader = Foo.class.getClassLoader();

    try
    {
      final URL catalogUrl = classLoader.getResource(catalogPath);
      final URI catalog = catalogUrl.toURI();

      if (catalog != null)
      {
        SchemaFactory schemaFactory =
          SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
        Schema schema = schemaFactory.newSchema();

        StreamSource source = new StreamSource(new File("xyzzy.xml"));
        Validator validator = schema.newValidator();

        validator.setProperty(catalogFile, catalog.toString());

        StringWriter writer = new StringWriter();
        StreamResult result = new StreamResult(writer);
        validator.validate(source, result);

        System.out.println(writer);
      }
    }
    catch (Exception e)
    {
      e.printStackTrace();
    }
  }
}

Catalog file ./foo/catalog.xml
<?xml version="1.0"?>
<!DOCTYPE catalog
PUBLIC "-//OASIS/DTD Entity Resolution XML Catalog V1.0//EN"
"http://www.oasis-open.org/comittees/entity/release/1.0/catalog.dtd">

<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">
  <uri name="urn:foo:bar:xyzzy.xsd:0.1"
       uri="schemas/xyzzy.xsd"/>
</catalog>

XSD schema file ./foo/schemas/xyzzy.xsd
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           targetNamespace="urn:foo:bar"
           xmlns:gazonk="urn:foo:bar"
           elementFormDefault="qualified">
  <xs:element name="xyzzy">
    <xs:complexType/>
  </xs:element>
</xs:schema>

Input XML file ./xyzzy.xml
<?xml version="1.0"?>
<gazonk:xyzzy xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
              xmlns:gazonk="urn:foo:bar"
              xsi:schemaLocation="urn:foo:bar:xyzzy.xsd:0.1"/>
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Introduce wrapper class for CatalogResolver (./foo/Resolver.java)
package foo;

import java.io.InputStream;

import javax.xml.catalog.CatalogResolver;
import javax.xml.transform.Source;

import org.w3c.dom.ls.LSInput;

import org.xml.sax.InputSource;


public class Resolver implements CatalogResolver
{
  private final CatalogResolver m_resolver;


  public Resolver(CatalogResolver resolver)
  {
    if (resolver != null)
    {
      m_resolver = resolver;
    }
    else
    {
      String message = "Wrapped resolver must not be null.";
      throw new IllegalArgumentException(message);
    }
  }

  public Source resolve(String href, String base)
  {
    return m_resolver.resolve(href, base);
  }

  public InputSource resolveEntity(String publicId, String systemId)
  {
    // Ensure systemId is not null.
    return m_resolver.resolveEntity(publicId,
                                    (systemId == null)? "" : systemId);
  }

  public InputStream resolveEntity(String publicId,
                                   String systemId,
                                   String baseUri,
                                   String namespace)
  {
    // Ensure systemId is not null.
    return m_resolver.resolveEntity(publicId,
                                    (systemId == null)? "" : systemId,
                                    baseUri,
                                    namespace);
  }

  public LSInput resolveResource(String type,
                                 String namespaceUri,
                                 String publicId,
                                 String systemId,
                                 String baseUri)
  {
    // Ensure both publicId and systemId are not null at the same time
    // before passing it on to the real resolver.
    if ((publicId == null) && (systemId == null))
    {
      String message = ("Missing namespace and schema location pair, " +
                         "only have namespace URI '" + namespaceUri +
                         "' which is not enough to go on when trying to " +
                         "locate the schema file...");
      throw new NullPointerException(message);
    }

    // Ensure systemId is not null.
    return m_resolver.resolveResource(type,
                                      namespaceUri,
                                      publicId,
                                      (systemId == null)? "" : systemId,
                                      baseUri);
  }
}

and modified variant of ./foo/Foo.java called ./foo/Bar.java that uses foo.Resolver
package foo;

import java.io.File;
import java.io.StringWriter;

import java.net.URL;
import java.net.URI;
import java.net.URISyntaxException;

import javax.xml.XMLConstants;
import javax.xml.catalog.CatalogFeatures;
import javax.xml.catalog.CatalogManager;
import javax.xml.catalog.CatalogResolver;
import javax.xml.transform.stream.StreamSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Schema;
import javax.xml.validation.Validator;

import org.w3c.dom.ls.LSInput;

public class Bar
{
  public static void main(String[] args)
  {
    final String catalogFile = CatalogFeatures.Feature.FILES.getPropertyName();
    final String catalogPath = "foo/catalog.xml";

    final ClassLoader classLoader = Foo.class.getClassLoader();

    try
    {
      final URL catalogUrl = classLoader.getResource(catalogPath);
      final URI catalog = catalogUrl.toURI();

      if (catalog != null)
      {
        CatalogFeatures features = CatalogFeatures.builder()
          //.with(Feature.FILES, catalog.toString())
          .with(CatalogFeatures.Feature.PREFER, "public")
          .with(CatalogFeatures.Feature.DEFER, "true")
          .with(CatalogFeatures.Feature.RESOLVE, "strict")
          .build();
        CatalogResolver resolver = CatalogManager.catalogResolver(features,
                                                                   catalog);
        Resolver wrapper = new Resolver(resolver);

        SchemaFactory schemaFactory =
          SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
        schemaFactory.setResourceResolver(wrapper);
        Schema schema = schemaFactory.newSchema();

        StreamSource source = new StreamSource(new File("xyzzy.xml"));
        Validator validator = schema.newValidator();

        validator.setProperty(catalogFile, catalog.toString());
        validator.setResourceResolver(wrapper);

        StringWriter writer = new StringWriter();
        StreamResult result = new StreamResult(writer);
        validator.validate(source, result);

        System.out.println(writer);
        /*
        */
      }
    }
    catch (Exception e)
    {
      e.printStackTrace();
    }
  }
}


FREQUENCY : always