8280373: Update Xalan serializer / SystemIDResolver to align with JDK…

…-8270492

Backport-of: c180070cb59b8e075376ae913c5db9a4ed868303

src/java.xml/share/classes/com/sun/org/apache/xml/internal/serializer/utils/SystemIDResolver.java

@@ -1,6 +1,5 @@
 /*
- * reserved comment block
- * DO NOT REMOVE OR ALTER!
+ * Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
  */
 /*
  * Licensed to the Apache Software Foundation (ASF) under one or more
@@ -42,6 +41,8 @@
  * used in com.sun.org.apache.xml.internal.serializer.
  *
  * @xsl.usage internal
+ *
+ * @LastModified: Jan 2022
  */
 public final class SystemIDResolver
 {
@@ -282,7 +283,7 @@ public static String getAbsoluteURI(String systemId)
   public static String getAbsoluteURI(String urlString, String base)
           throws TransformerException
   {
-    if (base == null)
+    if (base == null || base.length() == 0)
       return getAbsoluteURI(urlString);
 
     String absoluteBase = getAbsoluteURI(base);