Index: jackrabbit-core/src/main/java/org/apache/jackrabbit/core/NamespaceRegistryImpl.java
===================================================================
--- jackrabbit-core/src/main/java/org/apache/jackrabbit/core/NamespaceRegistryImpl.java	(revision 768998)
+++ jackrabbit-core/src/main/java/org/apache/jackrabbit/core/NamespaceRegistryImpl.java	(working copy)
@@ -20,6 +20,7 @@
 import org.apache.jackrabbit.core.cluster.NamespaceEventListener;
 import org.apache.jackrabbit.core.fs.FileSystem;
 import org.apache.jackrabbit.core.fs.FileSystemResource;
+import org.apache.jackrabbit.core.util.DefaultNamespaceUtil;
 import org.apache.jackrabbit.core.util.StringIndex;
 import org.apache.jackrabbit.spi.Name;
 import org.apache.jackrabbit.util.XMLChar;
@@ -56,7 +57,8 @@
     static {
         // reserved prefixes
         reservedPrefixes.add(Name.NS_XML_PREFIX);
-        reservedPrefixes.add(Name.NS_XMLNS_PREFIX);
+        reservedPrefixes.add(Name.NS_XMLNS_PREFIX); 
+        reservedPrefixes.add(Name.NS_DEFAULT_CONV_VALUE);
         // predefined (e.g. built-in) prefixes
         reservedPrefixes.add(Name.NS_REP_PREFIX);
         reservedPrefixes.add(Name.NS_JCR_PREFIX);
@@ -66,6 +68,7 @@
         // reserved namespace URI's
         reservedURIs.add(Name.NS_XML_URI);
         reservedURIs.add(Name.NS_XMLNS_URI);
+        reservedURIs.add(Name.NS_DEFAULT_CONV_VALUE);
         // predefined (e.g. built-in) namespace URI's
         reservedURIs.add(Name.NS_REP_URI);
         reservedURIs.add(Name.NS_JCR_URI);
@@ -128,7 +131,9 @@
      * @param uri the namespace uri
      * @param idx the index or <code>null</code>.
      */
-    private void map(String prefix, String uri, Integer idx) {
+    private void map(String prefix, String uri, Integer idx) {        
+        prefix = DefaultNamespaceUtil.convertToDefaultIfRequired(prefix);
+        uri = DefaultNamespaceUtil.convertToDefaultIfRequired(uri);        
         prefixToURI.put(prefix, uri);
         uriToPrefix.put(uri, prefix);
         if (!uriToIndex.containsKey(uri)) {
@@ -207,6 +212,9 @@
                         map(prefix, uri);
                     }
                 }
+                
+                addDefaultNamespaceIfNotFound();
+                
             } finally {
                 in.close();
             }
@@ -220,6 +228,18 @@
         }
     }
 
+    /**
+     * Verify that the default (empty) namespace exists. If it does
+     * not, add it.  This can happen if the existing namespace 
+     * property file has been created with the empty prefix and
+     * not the 'converted' value.
+     */
+    private void addDefaultNamespaceIfNotFound() {       
+        if (!prefixToURI.containsKey(Name.NS_EMPTY_PREFIX)) {
+            map(Name.NS_EMPTY_PREFIX, Name.NS_DEFAULT_URI);
+        }
+    }
+
     private void store() throws RepositoryException {
         FileSystemResource propFile =
                 new FileSystemResource(nsRegStore, NS_REG_RESOURCE);
@@ -233,7 +253,7 @@
             while (iter.hasNext()) {
                 String prefix = (String) iter.next();
                 String uri = (String) prefixToURI.get(prefix);
-                props.setProperty(prefix, uri);
+                setProperty(props, prefix, uri);
             }
 
             try {
@@ -260,7 +280,7 @@
             while (iter.hasNext()) {
                 String uri = (String) iter.next();
                 String index = uriToIndex.get(uri).toString();
-                props.setProperty(uri, index);
+                setProperty(props, uri, index);
             }
 
             try {
@@ -277,6 +297,23 @@
     }
 
     /**
+     * Adds a specific key/value pair into the properties object.  If the key/value
+     * pair represents the default namespace, the values will be converted into a
+     * different representation before storing in the properties.  The method
+     * {@link DefaultNamespaceUtil#convertToDefaultIfRequired(String)} should be called when reading
+     * information from a property object to properly 'undo' this conversion.
+     * 
+     * @param props Property object to store the key/value pair
+     * @param key Key that will be used when setting the property
+     * @param value Value of the property that is being set
+     */
+    private void setProperty(Properties props, String key, String value) {        
+        key = DefaultNamespaceUtil.convertToValueIfDefault(key);
+        value = DefaultNamespaceUtil.convertToValueIfDefault(value);          
+        props.setProperty(key, value);
+    }
+
+    /**
      * Set an event channel to inform about changes.
      *
      * @param eventChannel event channel
Index: jackrabbit-core/src/main/java/org/apache/jackrabbit/core/util/DefaultNamespaceUtil.java
===================================================================
--- jackrabbit-core/src/main/java/org/apache/jackrabbit/core/util/DefaultNamespaceUtil.java	(revision 0)
+++ jackrabbit-core/src/main/java/org/apache/jackrabbit/core/util/DefaultNamespaceUtil.java	(revision 0)
@@ -0,0 +1,66 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.jackrabbit.core.util;
+
+
+import org.apache.jackrabbit.spi.Name;
+
+/**
+ * Simple utility class that converts the default namespace/uri into a value 
+ * that can be used when storing information into property files. Added to
+ * resolve issues on IBM JDK 1.6 (see JIRA issue JCR-888).
+ */
+public class DefaultNamespaceUtil {
+
+    /**
+     * Converts the value into a non-empty string representation if the value
+     * provided is {@link Name#NS_DEFAULT_URI} or {@link Name#NS_EMPTY_PREFIX}.
+     * 
+     * @param value URI or prefix to convert if default.
+     * @return If the value is default, a non-empty string representation that
+     * should be used when storing into property files.  If not, the value
+     * will be returned.
+     */
+    public static String convertToValueIfDefault(String value) {
+        if (Name.NS_DEFAULT_URI.equals(value) || 
+                Name.NS_EMPTY_PREFIX.equals(value)) {
+            return Name.NS_DEFAULT_CONV_VALUE;
+        }
+        
+        return value;
+    }
+
+    /**
+     * Converts the value back into the empty string representing  
+     * {@link Name#NS_DEFAULT_URI} or {@link Name#NS_EMPTY_PREFIX} if the
+     * value is equal to the converted string returned from the
+     * {@link #convertToValueIfDefault(String)} method.  If the value is not 
+     * equal, it will be returned without modification.
+     *  
+     * @param value Value to check if it is the converted default namespace
+     * value.
+     * @return The default uri/empty prefix if the value provided was converted
+     * by this class previously.
+     */
+    public static String convertToDefaultIfRequired(String value) {
+        if (Name.NS_DEFAULT_CONV_VALUE.equals(value)) {
+            return Name.NS_DEFAULT_URI;
+        }
+        
+        return value;
+    }    
+}
Index: jackrabbit-core/src/test/java/org/apache/jackrabbit/core/util/DefaultNamespaceUtilTest.java
===================================================================
--- jackrabbit-core/src/test/java/org/apache/jackrabbit/core/util/DefaultNamespaceUtilTest.java	(revision 0)
+++ jackrabbit-core/src/test/java/org/apache/jackrabbit/core/util/DefaultNamespaceUtilTest.java	(revision 0)
@@ -0,0 +1,105 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.jackrabbit.core.util;
+
+import org.apache.jackrabbit.spi.Name;
+
+import junit.framework.TestCase;
+
+/**
+ * Unit test class to verify that the DefaultNamespaceUtil class properly
+ * converts the default URI/Namespace value "" into a constant and vice-versa
+ */
+public class DefaultNamespaceUtilTest extends TestCase {
+
+    /**
+     * Test that a non-default value sent to the utility class will not be
+     * modified.
+     */
+    public void testResolveNonDefaultToValue() {
+        String value = "testValue";
+
+        String actualValue = DefaultNamespaceUtil.convertToValueIfDefault(value);
+
+        assertEquals("Value should not be changed if it is not the default" +
+        		" URI/Namepace", value, actualValue);
+    }
+	
+    /**
+     * Test that the default URI will be converted into a different 
+     * value.
+     */
+    public void testResolveDefaultUriToValue() {
+        String value = Name.NS_DEFAULT_URI;
+        String actualValue = DefaultNamespaceUtil.convertToValueIfDefault(value);
+        
+        assertEquals("Default URI should be changed", 
+                Name.NS_DEFAULT_CONV_VALUE, actualValue);
+    }
+    
+    /**
+     * Test that the default prefix will be converted into a different 
+     * value.
+     */
+    public void testResolveDefaultPrefixToValue() {
+        String value = Name.NS_EMPTY_PREFIX;
+        String actualValue = DefaultNamespaceUtil.convertToValueIfDefault(value);
+        
+        assertEquals("Default value should be changed", 
+                Name.NS_DEFAULT_CONV_VALUE, actualValue);
+    }
+    
+    /**
+     * Test that a value that wasn't converted from the default namespace/uri
+     * isn't changed when restoring from a property.
+     */
+    public void testResolveNonDefaultFromValue() {
+        String value = "testValue";
+        
+        String actualValue = DefaultNamespaceUtil.convertToDefaultIfRequired(value);
+        
+        assertEquals("A non-default value should not be modified", value, actualValue);
+    }
+    
+    /**
+     * Test that the default URI value is provided when converting from the 
+     * modified value.
+     */
+    public void testResolveDefaultUriFromValue() {
+        String value = Name.NS_DEFAULT_CONV_VALUE;
+        String expValue = Name.NS_DEFAULT_URI;
+        
+        String actualValue = DefaultNamespaceUtil.convertToDefaultIfRequired(value);
+        
+        assertEquals("The value should be converted back into the default URI",
+                expValue, actualValue);
+    }
+    
+    /**
+     * Test that the empty prefix value is provided when converting from the 
+     * modified value.
+     */
+    public void testResolveDefaultPrefixFromValue() {
+        String value = Name.NS_DEFAULT_CONV_VALUE;
+        String expValue = Name.NS_EMPTY_PREFIX;
+        
+        String actualValue = DefaultNamespaceUtil.convertToDefaultIfRequired(value);
+        
+        assertEquals("The value should be converted back into the default URI",
+                expValue, actualValue);
+    }
+}
Index: jackrabbit-core/src/test/java/org/apache/jackrabbit/core/util/TestAll.java
===================================================================
--- jackrabbit-core/src/test/java/org/apache/jackrabbit/core/util/TestAll.java	(revision 768998)
+++ jackrabbit-core/src/test/java/org/apache/jackrabbit/core/util/TestAll.java	(working copy)
@@ -33,6 +33,7 @@
     public static Test suite() {
         TestSuite suite = new TestSuite("Utility tests");
         suite.addTestSuite(RepositoryLockTest.class);
+        suite.addTestSuite(DefaultNamespaceUtilTest.class);
         return suite;
     }
 }
Index: jackrabbit-spi/src/main/java/org/apache/jackrabbit/spi/Name.java
===================================================================
--- jackrabbit-spi/src/main/java/org/apache/jackrabbit/spi/Name.java	(revision 768998)
+++ jackrabbit-spi/src/main/java/org/apache/jackrabbit/spi/Name.java	(working copy)
@@ -36,8 +36,10 @@
 
     // default namespace (empty uri)
     public static final String NS_EMPTY_PREFIX = "";
-    public static final String NS_DEFAULT_URI = "";
-
+    public static final String NS_DEFAULT_URI = "";  
+    // converted string denoting the default uri/prefix (JCR-888)
+    public static final String NS_DEFAULT_CONV_VALUE = "jcrDefaultNamespace";
+    
     // reserved namespace for repository internal node types
     public static final String NS_REP_PREFIX = "rep";
     public static final String NS_REP_URI = "internal";
@@ -68,6 +70,7 @@
      * Empty array of <code>Name</code>
      */
     public static final Name[] EMPTY_ARRAY = new Name[0];
+    
 
     /**
      * Returns the local part of this <code>Name</code> object.