Fix NPE in InvocableHandlerMethod

Issue: SPR-13917

spring-web/src/main/java/org/springframework/web/method/support/InvocableHandlerMethod.java

@@ -223,7 +223,8 @@ public class InvocableHandlerMethod extends HandlerMethod {
 		}
 		catch (IllegalArgumentException ex) {
 			assertTargetBean(getBridgedMethod(), getBean(), args);
-			throw new IllegalStateException(getInvocationErrorMessage(ex.getMessage(), args), ex);
+			String message = (ex.getMessage() != null ? ex.getMessage() : "Illegal argument");
+			throw new IllegalStateException(getInvocationErrorMessage(message, args), ex);
 		}
 		catch (InvocationTargetException ex) {
 			// Unwrap for HandlerExceptionResolvers ...

spring-web/src/test/java/org/springframework/web/method/support/InvocableHandlerMethodTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -29,6 +29,7 @@ import org.springframework.web.bind.support.WebDataBinderFactory;
 import org.springframework.web.context.request.NativeWebRequest;
 import org.springframework.web.context.request.ServletWebRequest;
 
+import static org.hamcrest.Matchers.containsString;
 import static org.junit.Assert.*;
 
 /**
@@ -195,6 +196,28 @@ public class InvocableHandlerMethodTests {
 		}
 	}
 
+	// SPR-13917
+
+	@Test
+	public void invocationErrorMessage() throws Exception {
+		HandlerMethodArgumentResolverComposite composite = new HandlerMethodArgumentResolverComposite();
+		composite.addResolver(new StubArgumentResolver(double.class, null));
+
+		Method method = Handler.class.getDeclaredMethod("handle", double.class);
+		Object handler = new Handler();
+		InvocableHandlerMethod hm = new InvocableHandlerMethod(handler, method);
+		hm.setHandlerMethodArgumentResolvers(composite);
+
+		try {
+			hm.invokeForRequest(this.webRequest, new ModelAndViewContainer());
+			fail();
+		}
+		catch (IllegalStateException ex) {
+			assertThat(ex.getMessage(), containsString("Illegal argument"));
+		}
+	}
+
+
 	private void invokeExceptionRaisingHandler(Throwable expected) throws Exception {
 		Method method = ExceptionRaisingHandler.class.getDeclaredMethod("raiseException");
 		Object handler = new ExceptionRaisingHandler(expected);
@@ -209,6 +232,9 @@ public class InvocableHandlerMethodTests {
 		public String handle(Integer intArg, String stringArg) {
 			return intArg + "-" + stringArg;
 		}
+
+		public void handle(double amount) {
+		}
 	}