Use null-aware operators to clean up the code

pkg/analyzer/lib/src/generated/source_io.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.source_io;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/java_core.dart';
@@ skipping 158 matching lines @@
    * The cached encoding for this source.
    */
   String _encoding;
 
   /**
    * Initialize a newly created source object to represent the given [file]. If
    * a [uri] is given, then it will be used as the URI from which the source was
    * derived, otherwise a `file:` URI will be created based on the [file].
    */
   FileBasedSource(JavaFile file, [Uri uri])
-      : this.uri = (uri == null ? file.toURI() : uri),
+      : this.uri = uri ?? file.toURI(),
         this.file = file,
         id = _idTable.putIfAbsent(
-            '${uri == null ? file.toURI() : uri}@${file.getPath()}',
-            () => _idTable.length);
+            '${uri ?? file.toURI()}@${file.getPath()}', () => _idTable.length);
 
   @override
   TimestampedData<String> get contents {
     return PerformanceStatistics.io.makeCurrentWhile(() {
       return contentsFromFile;
     });
   }
 
   /**
    * Get the contents and timestamp of the underlying file.
@@ skipping 68 matching lines @@
   /**
    * The name of the `file` scheme.
    */
   static String FILE_SCHEME = "file";
 
   @override
   Source resolveAbsolute(Uri uri, [Uri actualUri]) {
     if (!isFileUri(uri)) {
       return null;
     }
-    return new FileBasedSource(
-        new JavaFile.fromUri(uri), actualUri != null ? actualUri : uri);
+    return new FileBasedSource(new JavaFile.fromUri(uri), actualUri ?? uri);
   }
 
   @override
   Uri restoreAbsolute(Source source) {
     return new Uri.file(source.fullName);
   }
 
   /**
    * Return `true` if the given URI is a `file` URI.
    *
@@ skipping 165 matching lines @@
           return new FileBasedSource(canonicalFile, actualUri);
         }
         if (_isSelfReference(packagesDirectory, canonicalFile)) {
           uri = canonicalFile.toURI();
         }
         return new FileBasedSource(canonicalFile, uri);
       }
     }
     return new FileBasedSource(
         getCanonicalFile(_packagesDirectories[0], pkgName, relPath),
-        actualUri != null ? actualUri : uri);
+        actualUri ?? uri);
   }
 
   @override
   Uri restoreAbsolute(Source source) {
     String sourceUri = _toFileUri(source.fullName);
     for (JavaFile packagesDirectory in _packagesDirectories) {
       List<JavaFile> pkgFolders = packagesDirectory.listFiles();
       if (pkgFolders != null) {
         for (JavaFile pkgFolder in pkgFolders) {
           try {
@@ skipping 68 matching lines @@
 
   @override
   Source resolveAbsolute(Uri uri, [Uri actualUri]) {
     String rootPath = _rootDirectory.toURI().path;
     String uriPath = uri.path;
     if (uriPath != null && uriPath.startsWith(rootPath)) {
       String filePath = uri.path.substring(rootPath.length);
       for (JavaFile dir in _relativeDirectories) {
         JavaFile file = new JavaFile.relative(dir, filePath);
         if (file.exists()) {
-          return new FileBasedSource(file, actualUri != null ? actualUri : uri);
+          return new FileBasedSource(file, actualUri ?? uri);
         }
       }
     }
     return null;
   }
 
   /**
    * Return `true` if the given URI is a `file` URI.
    *
    * @param uri the URI being tested
    * @return `true` if the given URI is a `file` URI
    */
   static bool isFileUri(Uri uri) => uri.scheme == FILE_SCHEME;
 }