Allow ant task to take empty groups and excludedgroups properties, supressing the -groups flag from the testNG parameter list
This means that a generic TestNG target can have its grouping behaviour modified by properties set before the target is invoked
diff --git a/src/main/org/testng/TestNGAntTask.java b/src/main/org/testng/TestNGAntTask.java
index 62b64aa..05021f5 100644
--- a/src/main/org/testng/TestNGAntTask.java
+++ b/src/main/org/testng/TestNGAntTask.java
@@ -432,12 +432,12 @@
       argv.add(srcPath);
     }
     
-    if(null != m_includedGroups) {
+    if(null != m_includedGroups&&!"".equals(m_includedGroups)) {
       argv.add(TestNGCommandLineArgs.GROUPS_COMMAND_OPT);
       argv.add(m_includedGroups);
     }
     
-    if(null != m_excludedGroups) {
+    if(null != m_excludedGroups&&!"".equals(m_excludedGroups)) {
       argv.add(TestNGCommandLineArgs.EXCLUDED_GROUPS_COMMAND_OPT);
       argv.add(m_excludedGroups);
     }