SPR-8561 Permit null values for simple controller method arguments types without annotations.

org.springframework.web/src/main/java/org/springframework/web/method/annotation/support/RequestParamMethodArgumentResolver.java

@@ -194,7 +194,7 @@ public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethod
 	private class RequestParamNamedValueInfo extends NamedValueInfo {
 
 		private RequestParamNamedValueInfo() {
-			super("", true, ValueConstants.DEFAULT_NONE);
+			super("", false, ValueConstants.DEFAULT_NONE);
 		}
 		
 		private RequestParamNamedValueInfo(RequestParam annotation) {

org.springframework.web/src/test/java/org/springframework/web/method/annotation/support/RequestParamMethodArgumentResolverTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.web.method.annotation.support;
 
+import static org.junit.Assert.*;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -221,6 +222,14 @@ public class RequestParamMethodArgumentResolverTests {
 		assertEquals("plainValue", result);
 	}
 
+	// SPR-8561
+	
+	@Test
+	public void resolveSimpleTypeParamToNull() throws Exception {
+		Object result = resolver.resolveArgument(paramStringNotAnnot, null, webRequest, null);
+		assertNull(result);
+	}
+
 	public void params(@RequestParam(value = "name", defaultValue = "bar") String param1,
 					   @RequestParam("name") String[] param2,
 					   @RequestParam("name") Map<?, ?> param3,