Added conditions to disregard the returned output from an extension URI resolver if it returns null.
diff --git a/plugins/org.eclipse.wst.common.uriresolver/src/org/eclipse/wst/common/uriresolver/internal/ExtensibleURIResolver.java b/plugins/org.eclipse.wst.common.uriresolver/src/org/eclipse/wst/common/uriresolver/internal/ExtensibleURIResolver.java
index a16713a..e9bdabf 100644
--- a/plugins/org.eclipse.wst.common.uriresolver/src/org/eclipse/wst/common/uriresolver/internal/ExtensibleURIResolver.java
+++ b/plugins/org.eclipse.wst.common.uriresolver/src/org/eclipse/wst/common/uriresolver/internal/ExtensibleURIResolver.java
@@ -64,7 +64,11 @@
 		for (Iterator i = resolverRegistry.getMatchingURIResolvers(list, URIResolverExtensionRegistry.STAGE_PRENORMALIZATION).iterator(); i.hasNext();)
 		{
 			URIResolverExtension resolver = (URIResolverExtension) i.next();
-			result = resolver.resolve(project, baseLocation, publicId, result);
+			String tempresult = resolver.resolve(project, baseLocation, publicId, result);
+			if(tempresult != null)
+			{
+			  result = tempresult;
+			}
 		}
 
 		// normalize the uri
@@ -77,7 +81,11 @@
 		for (Iterator i = resolverRegistry.getMatchingURIResolvers(list, URIResolverExtensionRegistry.STAGE_POSTNORMALIZATION).iterator(); i.hasNext();)
 		{
 			URIResolverExtension resolver = (URIResolverExtension) i.next();
-			result = resolver.resolve(project, baseLocation, publicId, result);
+			String tempresult = resolver.resolve(project, baseLocation, publicId, result);
+			if(tempresult != null)
+			{
+			  result = tempresult;
+			}
 		}
 
 		return result;