Always preserve dominant node value (even if empty)

This closes codehaus-plexus#216

Author: kwin

src/main/java/org/codehaus/plexus/util/xml/Xpp3DomUtils.java

@@ -95,8 +95,6 @@ public void writeToSerializer( String namespace, XmlSerializer serializer, Xpp3D
      *   </ol></li>
      * <li> If mergeSelf == true
      *   <ol type="A">
-     *   <li> if the dominant root node's value is empty, set it to the recessive root node's value</li>
-     *   <li> For each attribute in the recessive root node which is not set in the dominant root node, set it.</li>
      *   <li> Determine whether children from the recessive DOM will be merged or appended to the dominant DOM as
      *        siblings (flag=mergeChildren).
      *     <ol type="i">
@@ -140,12 +138,6 @@ private static void mergeIntoXpp3Dom( Xpp3Dom dominant, Xpp3Dom recessive, Boole
 
         if ( mergeSelf )
         {
-            if ( isEmpty( dominant.getValue() ) && !isEmpty( recessive.getValue() ) )
-            {
-                dominant.setValue( recessive.getValue() );
-                dominant.setInputLocation( recessive.getInputLocation() );
-            }
-
             String[] recessiveAttrs = recessive.getAttributeNames();
             for ( String attr : recessiveAttrs )
             {

src/test/java/org/codehaus/plexus/util/xml/Xpp3DomUtilsTest.java

@@ -18,9 +18,11 @@
 
 import static org.junit.Assert.assertEquals;
 
+import java.io.IOException;
 import java.io.StringReader;
 
 import org.codehaus.plexus.util.xml.pull.XmlPullParser;
+import org.codehaus.plexus.util.xml.pull.XmlPullParserException;
 import org.junit.Test;
 
 /**
@@ -111,7 +113,21 @@ public void testCombineKeys()
         assertEquals( "RHS", mergeResult.getChildren( "property" )[2].getChild( "value" ).getValue() );
         assertEquals( "right", p2.getChild( "value" ).getInputLocation() );
     }
-    
+
+    @Test
+    public void testPreserveDominantEmptyNode() throws XmlPullParserException, IOException
+    {
+        String lhs = "<parameter></parameter>";
+
+        String rhs = "<parameter>recessive</parameter>";
+
+        Xpp3Dom leftDom = Xpp3DomBuilder.build( new StringReader( lhs ), new FixedInputLocationBuilder( "left" ) );
+        Xpp3Dom rightDom = Xpp3DomBuilder.build( new StringReader( rhs ), new FixedInputLocationBuilder( "right" ) );
+
+        Xpp3Dom mergeResult = Xpp3DomUtils.mergeXpp3Dom( leftDom, rightDom, true );
+        assertEquals( "", mergeResult.getValue() );
+    }
+
     private static class FixedInputLocationBuilder
         implements Xpp3DomBuilder.InputLocationBuilder
     {