Polish UsernamePasswordAuthenticationFilter method

Closes gh-10970

web/src/main/java/org/springframework/security/web/authentication/UsernamePasswordAuthenticationFilter.java

@@ -75,8 +75,7 @@ public class UsernamePasswordAuthenticationFilter extends AbstractAuthentication
 			throw new AuthenticationServiceException("Authentication method not supported: " + request.getMethod());
 		}
 		String username = obtainUsername(request);
-		username = (username != null) ? username : "";
-		username = username.trim();
+		username = (username != null) ? username.trim() : "";
 		String password = obtainPassword(request);
 		password = (password != null) ? password : "";
 		UsernamePasswordAuthenticationToken authRequest = UsernamePasswordAuthenticationToken.unauthenticated(username,