Fix exception mock request builder

Issue: SPR-11043

spring-test-mvc/src/main/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilder.java

@@ -593,9 +593,8 @@ public class MockHttpServletRequestBuilder implements RequestBuilder, Mergeable
 
 			for (Entry<String, List<String>> entry : this.uriComponents.getQueryParams().entrySet()) {
 				for (String value : entry.getValue()) {
-					request.addParameter(
-							UriUtils.decode(entry.getKey(), "UTF-8"),
-							UriUtils.decode(value, "UTF-8"));
+					value = (value != null) ? UriUtils.decode(value, "UTF-8") : null;
+					request.addParameter(UriUtils.decode(entry.getKey(), "UTF-8"), value);
 				}
 			}
 		}

spring-test-mvc/src/test/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilderTests.java

@@ -228,6 +228,19 @@ public class MockHttpServletRequestBuilderTests {
 		assertEquals("bar=baz", request.getParameter("foo"));
 	}
 
+	// SPR-11043
+
+	@Test
+	public void requestParameterFromQueryNull() throws Exception {
+		this.builder = new MockHttpServletRequestBuilder(HttpMethod.GET, "/?foo");
+
+		MockHttpServletRequest request = this.builder.buildRequest(this.servletContext);
+		Map<String, String[]> parameterMap = request.getParameterMap();
+
+		assertArrayEquals(new String[]{null}, parameterMap.get("foo"));
+		assertEquals("foo", request.getQueryString());
+	}
+
 	@Test
 	public void acceptHeader() throws Exception {
 		this.builder.accept(MediaType.TEXT_HTML, MediaType.APPLICATION_XML);