Fix analysis hints (#2014)

Author: keertip

lib/src/model.dart

@@ -5671,7 +5671,7 @@ class PackageGraph {
       lib ??= Library(e.enclosingElement.library, packageGraph);
       // (TODO:keertip) Find a better way to exclude members of extensions
       //  when libraries are specified using the "--include" flag
-      if (lib?.isDocumented) {
+      if (lib?.isDocumented == true) {
         return ModelElement.from(e, lib, packageGraph);
       }
     }

test/model_test.dart

@@ -2100,13 +2100,12 @@ void main() {
   });
 
   group('Extension', () {
-    Extension ext, anExt, fancyList;
+    Extension ext, fancyList;
     Method s;
     List<Extension> extensions;
 
     setUpAll(() {
       ext = exLibrary.extensions.firstWhere((e) => e.name == 'AppleExtension');
-      anExt = exLibrary.extensions.firstWhere((e) => e.name == 'AnExtension');
       fancyList = exLibrary.extensions.firstWhere((e) => e.name == 'FancyList');
       extensions = exLibrary.publicExtensions.toList();
     });