cleanup: migrate from .expand to .followedBy

Author: kevmoo

json_serializable/lib/src/json_serializable_generator.dart

@@ -91,8 +91,8 @@ class JsonSerializableGenerator
       new JsonSerializableGenerator(
           useWrappers: useWrappers,
           anyMap: anyMap,
-          typeHelpers: new List.unmodifiable(
-              [typeHelpers, _defaultHelpers].expand((e) => e)));
+          typeHelpers:
+              new List.unmodifiable(typeHelpers.followedBy(_defaultHelpers)));
 
   @override
   Future<String> generateForAnnotatedElement(

json_serializable/lib/src/shared_checkers.dart

@@ -63,8 +63,8 @@ DartType _getImplementationType(DartType type, TypeChecker checker) {
   if (checker.isExactlyType(type)) return type;
 
   if (type is InterfaceType) {
-    var match = [type.interfaces, type.mixins]
-        .expand((e) => e)
+    var match = type.interfaces
+        .followedBy(type.mixins)
         .map((type) => _getImplementationType(type, checker))
         .firstWhere((value) => value != null, orElse: () => null);
 

json_serializable/lib/src/type_helpers/json_helper.dart

@@ -102,8 +102,8 @@ MethodElement _getMethod(DartType type, String methodName) {
       return method;
     }
 
-    var match = [type.interfaces, type.mixins]
-        .expand((e) => e)
+    var match = type.interfaces
+        .followedBy(type.mixins)
         .map((type) => _getMethod(type, methodName))
         .firstWhere((value) => value != null, orElse: () => null);