diff --git a/WHATSNEW b/WHATSNEW
index ebf7115a9..d865037bf 100644
--- a/WHATSNEW
+++ b/WHATSNEW
@@ -138,6 +138,10 @@ Fixed bugs:
    from a resource or string explicitly.
    Bugzilla Report 49587.
 
+ * Project#setDefault threw an excpetion when null was passed in as
+   argument, even though the javadoc says, null is a valid value.
+   Bugzilla Report 49803.
+
 Other changes:
 --------------
 
diff --git a/src/main/org/apache/tools/ant/Project.java b/src/main/org/apache/tools/ant/Project.java
index 843e81093..27f5f3289 100644
--- a/src/main/org/apache/tools/ant/Project.java
+++ b/src/main/org/apache/tools/ant/Project.java
@@ -729,7 +729,9 @@ public class Project implements ResourceFactory {
      *                      no default target.
      */
     public void setDefault(String defaultTarget) {
-        setUserProperty(MagicNames.PROJECT_DEFAULT_TARGET, defaultTarget);
+        if (defaultTarget != null) {
+            setUserProperty(MagicNames.PROJECT_DEFAULT_TARGET, defaultTarget);
+        }
         this.defaultTarget = defaultTarget;
     }