Use null-aware operators to clean up the code

pkg/analyzer/lib/src/generated/java_core.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.src.generated.java_core;
 
 final Stopwatch nanoTimeStopwatch = new Stopwatch();
 
 /**
  * Inserts the given arguments into [pattern].
@@ skipping 19 matching lines @@
 String formatList(String pattern, List<Object> arguments) {
   if (arguments == null || arguments.isEmpty) {
     assert(!pattern.contains(new RegExp(r'\{(\d+)\}')));
     return pattern;
   }
   return pattern.replaceAllMapped(new RegExp(r'\{(\d+)\}'), (match) {
     String indexStr = match.group(1);
     int index = int.parse(indexStr);
     Object arg = arguments[index];
     assert(arg != null);
-    return arg != null ? arg.toString() : null;
+    return arg?.toString();
   });
 }
 
 /// Parses given string to [Uri], throws [URISyntaxException] if invalid.
 Uri parseUriWithException(String str) {
   Uri uri;
   try {
     uri = Uri.parse(str);
   } on FormatException catch (e) {
     throw new URISyntaxException(e.toString());
@@ skipping 316 matching lines @@
 
 class UnsupportedOperationException extends JavaException {
   UnsupportedOperationException([message = ""]) : super(message);
 }
 
 class URISyntaxException implements Exception {
   final String message;
   URISyntaxException(this.message);
   String toString() => "URISyntaxException: $message";
 }