fixed setRootObject check in StandardEvaluationContext (SPR-8241)

org.springframework.expression/src/main/java/org/springframework/expression/spel/support/StandardEvaluationContext.java

 /*
- * Copyright 2002-2009 the original author or authors.
+ * Copyright 2002-2011 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -80,18 +80,14 @@ public class StandardEvaluationContext implements EvaluationContext {
 	}
 
 
-	public void setRootObject(Object rootObject) {
-		if (this.rootObject == null) {
-			this.rootObject = TypedValue.NULL;
-		} else {
-			this.rootObject = new TypedValue(rootObject);//, TypeDescriptor.forObject(rootObject));
-		}
-	}
-
 	public void setRootObject(Object rootObject, TypeDescriptor typeDescriptor) {
 		this.rootObject = new TypedValue(rootObject, typeDescriptor);
 	}
 
+	public void setRootObject(Object rootObject) {
+		this.rootObject = (rootObject != null ? new TypedValue(rootObject) : TypedValue.NULL);
+	}
+
 	public TypedValue getRootObject() {
 		return this.rootObject;
 	}