Exclude null requestURI in MHSR.getRequestURL()

This commit undoes the changes made in ec5d81e78e and ensures that the
getRequestURL() method in MockHttpServletRequest does not include the
String "null" for a null requestURI by first checking if the requestURI
contains text before including it in the composed URL.

Issue: SPR-10643

spring-test/src/test/java/org/springframework/mock/web/MockHttpServletRequestTests.java

@@ -211,6 +211,13 @@ public class MockHttpServletRequestTests {
 		assertEquals("http://localhost", requestURL.toString());
 	}
 
+	@Test
+	public void getRequestURLWithNullRequestUri() {
+		request.setRequestURI(null);
+		StringBuffer requestURL = request.getRequestURL();
+		assertEquals("http://localhost", requestURL.toString());
+	}
+
 	@Test
 	public void getRequestURLWithDefaultsAndHttps() {
 		request.setScheme("https");