empty string handling

spring-webflow/src/main/java/org/springframework/webflow/action/ResultObjectBasedEventFactory.java

@@ -17,6 +17,7 @@ package org.springframework.webflow.action;
 
 import org.springframework.core.JdkVersion;
 import org.springframework.core.enums.LabeledEnum;
+import org.springframework.util.StringUtils;
 import org.springframework.webflow.execution.Event;
 import org.springframework.webflow.execution.RequestContext;
 
@@ -81,7 +82,13 @@ public class ResultObjectBasedEventFactory extends EventFactorySupport implement
 			String eventId = EnumUtils.getEnumName(resultObject);
 			return event(source, eventId, getResultAttributeName(), resultObject);
 		} else if (isString(resultObject.getClass())) {
-			return event(source, (String) resultObject);
+			String resultString = (String) resultObject;
+			if (StringUtils.hasText(resultString)) {
+				return event(source, resultString);
+			} else {
+				// treat an empty string as the null event
+				return event(source, getNullEventId());
+			}
 		} else if (isEvent(resultObject.getClass())) {
 			return (Event) resultObject;
 		} else {

spring-webflow/src/test/java/org/springframework/webflow/action/EvaluateActionTests.java

@@ -34,6 +34,20 @@ public class EvaluateActionTests extends TestCase {
 		assertEquals("bar", result.getId());
 	}
 
+	public void testEvaluateExpressionEmptyStringResult() throws Exception {
+		EvaluateAction action = new EvaluateAction(new StaticExpression(""), null);
+		MockRequestContext context = new MockRequestContext();
+		Event result = action.execute(context);
+		assertEquals("null", result.getId());
+	}
+
+	public void testEvaluateExpressionNullResult() throws Exception {
+		EvaluateAction action = new EvaluateAction(new StaticExpression(null), null);
+		MockRequestContext context = new MockRequestContext();
+		Event result = action.execute(context);
+		assertEquals("success", result.getId());
+	}
+
 	public void testEvaluateExpressionResultExposer() throws Exception {
 		StaticExpression resultExpression = new StaticExpression("");
 		EvaluateAction action = new EvaluateAction(new StaticExpression("bar"), new ActionResultExposer(