Properly detect null value params in params conditions

Issue: SPR-15831

spring-webflux/src/test/java/org/springframework/web/reactive/result/condition/ParamsRequestConditionTests.java

@@ -51,6 +51,12 @@ public class ParamsRequestConditionTests {
 		assertNotNull(condition.getMatchingCondition(get("/path?foo=").toExchange()));
 	}
 
+	@Test // SPR-15831
+	public void paramPresentNullValue() throws Exception {
+		ParamsRequestCondition condition = new ParamsRequestCondition("foo");
+		assertNotNull(condition.getMatchingCondition(get("/path?foo").toExchange()));
+	}
+
 	@Test
 	public void paramPresentNoMatch() throws Exception {
 		ParamsRequestCondition condition = new ParamsRequestCondition("foo");

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/condition/ParamsRequestCondition.java

@@ -142,7 +142,8 @@ public final class ParamsRequestCondition extends AbstractRequestCondition<Param
 
 		@Override
 		protected boolean matchName(HttpServletRequest request) {
-			return WebUtils.hasSubmitParameter(request, this.name);
+			return WebUtils.hasSubmitParameter(request, this.name) ||
+					request.getParameterMap().containsKey(this.name);
 		}
 
 		@Override

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/condition/ParamsRequestConditionTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -23,7 +23,11 @@ import org.junit.Test;
 import org.springframework.mock.web.test.MockHttpServletRequest;
 import org.springframework.web.servlet.mvc.condition.ParamsRequestCondition.ParamExpression;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
 
 /**
  * Unit tests for {@link ParamsRequestCondition}.
@@ -48,6 +52,14 @@ public class ParamsRequestConditionTests {
 		assertNotNull(new ParamsRequestCondition("foo").getMatchingCondition(request));
 	}
 
+	@Test // SPR-15831
+	public void paramPresentNullValue() {
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		request.addParameter("foo", (String) null);
+
+		assertNotNull(new ParamsRequestCondition("foo").getMatchingCondition(request));
+	}
+
 	@Test
 	public void paramPresentNoMatch() {
 		MockHttpServletRequest request = new MockHttpServletRequest();