Use null-aware operators to clean up the code

pkg/analyzer/lib/src/context/source.dart

Index: pkg/analyzer/lib/src/context/source.dart
diff --git a/pkg/analyzer/lib/src/context/source.dart b/pkg/analyzer/lib/src/context/source.dart
index 3a22291e45fa8e55b1b0b853047a97e16c98273d..32792df81f036f03d3621acfd27d54c6115fda9a 100644
--- a/pkg/analyzer/lib/src/context/source.dart
+++ b/pkg/analyzer/lib/src/context/source.dart
@@ -53,9 +53,8 @@ class SourceFactoryImpl implements SourceFactory {
    */
   SourceFactoryImpl(this.resolvers,
       [this._packages, ResourceProvider resourceProvider])
-      : _resourceProvider = resourceProvider != null
-            ? resourceProvider
-            : PhysicalResourceProvider.INSTANCE;
+      : _resourceProvider =
+            resourceProvider ?? PhysicalResourceProvider.INSTANCE;
 
   /**
    * Return the [DartSdk] associated with this [SourceFactory], or `null` if
@@ -105,7 +104,7 @@ class SourceFactoryImpl implements SourceFactory {
     // Default to the PackageMapUriResolver.
     PackageMapUriResolver resolver = resolvers
         .firstWhere((r) => r is PackageMapUriResolver, orElse: () => null);
-    return resolver != null ? resolver.packageMap : null;
+    return resolver?.packageMap;
   }
 
   /**