Xpp3DomUtils#mergeIntoXpp3Dom() must not override the dominant value in case it is empty (#216)

This fixes #216 and closes #217

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

@@ -115,7 +115,7 @@ public void testCombineKeys()
     }
 
     @Test
-    public void testOverwriteDominantBlankValue() throws XmlPullParserException, IOException {
+    public void testPreserveDominantBlankValue() throws XmlPullParserException, IOException {
         String lhs = "<parameter xml:space=\"preserve\"> </parameter>";
 
         String rhs = "<parameter>recessive</parameter>";
@@ -127,6 +127,20 @@ public void testOverwriteDominantBlankValue() throws XmlPullParserException, IOE
         assertEquals( " ", mergeResult.getValue() );
     }
 
+    @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() );
+    }
+
     @Test
     public void testIsNotEmptyNegatesIsEmpty()
     {