[Dart] Avoid redundant null checking in fromJson (#3632)

* Move dart null checks inside mustache type checks

- removed surrounding null check
- added a conditional expression to each case except the redundant one

* Run shell scripts so CIs can verify the change

Author: nickmeinhold

modules/openapi-generator/src/main/resources/dart2/class.mustache

@@ -16,51 +16,63 @@ class {{classname}} {
   {{classname}}.fromJson(Map<String, dynamic> json) {
     if (json == null) return;
   {{#vars}}
-    if (json['{{baseName}}'] == null) {
-      {{name}} = null;
-    } else {
   {{#isDateTime}}
-      {{name}} = DateTime.parse(json['{{baseName}}']);
+    {{name}} = (json['{{baseName}}'] == null) ?
+      null :
+      DateTime.parse(json['{{baseName}}']);
   {{/isDateTime}}
   {{#isDate}}
-      {{name}} = DateTime.parse(json['{{baseName}}']);
+    {{name}} = (json['{{baseName}}'] == null) ?
+      null :
+      DateTime.parse(json['{{baseName}}']);
   {{/isDate}}
   {{^isDateTime}}
   {{^isDate}}
     {{#complexType}}
       {{#isListContainer}}
-      {{name}} = {{complexType}}.listFromJson(json['{{baseName}}']);
+    {{name}} = (json['{{baseName}}'] == null) ?
+      null :
+      {{complexType}}.listFromJson(json['{{baseName}}']);
       {{/isListContainer}}
       {{^isListContainer}}
       {{#isMapContainer}}
-      {{name}} = {{complexType}}.mapFromJson(json['{{baseName}}']);
+    {{name}} = (json['{{baseName}}'] == null) ?
+      null :
+      {{complexType}}.mapFromJson(json['{{baseName}}']);
       {{/isMapContainer}}
       {{^isMapContainer}}
-      {{name}} = {{complexType}}.fromJson(json['{{baseName}}']);
+    {{name}} = (json['{{baseName}}'] == null) ?
+      null :
+      {{complexType}}.fromJson(json['{{baseName}}']);
       {{/isMapContainer}}
       {{/isListContainer}}
     {{/complexType}}
     {{^complexType}}
       {{#isListContainer}}
-      {{name}} = (json['{{baseName}}'] as List).cast<{{items.datatype}}>();
+    {{name}} = (json['{{baseName}}'] == null) ?
+      null :
+      (json['{{baseName}}'] as List).cast<{{items.datatype}}>();
       {{/isListContainer}}
       {{^isListContainer}}
         {{#isMapContainer}}
-          {{name}} = (json['{{baseName}}'] as Map).cast<String, {{items.datatype}}>();
+    {{name}} = (json['{{baseName}}'] == null) ?
+      null :
+      (json['{{baseName}}'] as Map).cast<String, {{items.datatype}}>();
         {{/isMapContainer}}
         {{^isMapContainer}}
-	{{#isDouble}}
-          {{name}} = json['{{baseName}}'].toDouble();
-	{{/isDouble}}
-	{{^isDouble}}
-          {{name}} = json['{{baseName}}'];
-	{{/isDouble}}
+          {{#isDouble}}
+    {{name}} = (json['{{baseName}}'] == null) ?
+      null :
+      json['{{baseName}}'].toDouble();
+          {{/isDouble}}
+          {{^isDouble}}
+    {{name}} = json['{{baseName}}'];
+          {{/isDouble}}
         {{/isMapContainer}}
       {{/isListContainer}}
     {{/complexType}}
   {{/isDate}}
   {{/isDateTime}}
-    }
   {{/vars}}
   }
 

samples/client/petstore/dart/flutter_petstore/openapi/lib/model/api_response.dart

@@ -2,11 +2,11 @@ part of openapi.api;
 
 class ApiResponse {
 
-  int code = null;
+    int code = null;
 
-  String type = null;
+    String type = null;
 
-  String message = null;
+    String message = null;
   ApiResponse();
 
   @override
@@ -16,21 +16,9 @@ class ApiResponse {
 
   ApiResponse.fromJson(Map<String, dynamic> json) {
     if (json == null) return;
-    if (json['code'] == null) {
-      code = null;
-    } else {
-      code = json['code'];
-    }
-    if (json['type'] == null) {
-      type = null;
-    } else {
-      type = json['type'];
-    }
-    if (json['message'] == null) {
-      message = null;
-    } else {
-      message = json['message'];
-    }
+    code = json['code'];
+    type = json['type'];
+    message = json['message'];
   }
 
   Map<String, dynamic> toJson() {

samples/client/petstore/dart/flutter_petstore/openapi/lib/model/category.dart

@@ -2,9 +2,9 @@ part of openapi.api;
 
 class Category {
 
-  int id = null;
+    int id = null;
 
-  String name = null;
+    String name = null;
   Category();
 
   @override
@@ -14,16 +14,8 @@ class Category {
 
   Category.fromJson(Map<String, dynamic> json) {
     if (json == null) return;
-    if (json['id'] == null) {
-      id = null;
-    } else {
-      id = json['id'];
-    }
-    if (json['name'] == null) {
-      name = null;
-    } else {
-      name = json['name'];
-    }
+    id = json['id'];
+    name = json['name'];
   }
 
   Map<String, dynamic> toJson() {

samples/client/petstore/dart/flutter_petstore/openapi/lib/model/inline_object.dart

@@ -2,9 +2,9 @@ part of openapi.api;
 
 class InlineObject {
   /* Updated name of the pet */
-  String name = null;
+    String name = null;
   /* Updated status of the pet */
-  String status = null;
+    String status = null;
   InlineObject();
 
   @override
@@ -14,16 +14,8 @@ class InlineObject {
 
   InlineObject.fromJson(Map<String, dynamic> json) {
     if (json == null) return;
-    if (json['name'] == null) {
-      name = null;
-    } else {
-          name = json['name'];
-    }
-    if (json['status'] == null) {
-      status = null;
-    } else {
-          status = json['status'];
-    }
+    name = json['name'];
+    status = json['status'];
   }
 
   Map<String, dynamic> toJson() {

samples/client/petstore/dart/flutter_petstore/openapi/lib/model/inline_object1.dart

@@ -2,9 +2,9 @@ part of openapi.api;
 
 class InlineObject1 {
   /* Additional data to pass to server */
-  String additionalMetadata = null;
+    String additionalMetadata = null;
   /* file to upload */
-  MultipartFile file = null;
+    MultipartFile file = null;
   InlineObject1();
 
   @override
@@ -14,16 +14,10 @@ class InlineObject1 {
 
   InlineObject1.fromJson(Map<String, dynamic> json) {
     if (json == null) return;
-    if (json['additionalMetadata'] == null) {
-      additionalMetadata = null;
-    } else {
-          additionalMetadata = json['additionalMetadata'];
-    }
-    if (json['file'] == null) {
-      file = null;
-    } else {
-      file = File.fromJson(json['file']);
-    }
+    additionalMetadata = json['additionalMetadata'];
+    file = (json['file'] == null) ?
+      null :
+      File.fromJson(json['file']);
   }
 
   Map<String, dynamic> toJson() {

samples/client/petstore/dart/flutter_petstore/openapi/lib/model/order.dart

@@ -2,18 +2,18 @@ part of openapi.api;
 
 class Order {
 
-  int id = null;
+    int id = null;
 
-  int petId = null;
+    int petId = null;
 
-  int quantity = null;
+    int quantity = null;
 
-  DateTime shipDate = null;
+    DateTime shipDate = null;
   /* Order Status */
-  String status = null;
+    String status = null;
   //enum statusEnum {  placed,  approved,  delivered,  };{
 
-  bool complete = false;
+    bool complete = false;
   Order();
 
   @override
@@ -23,36 +23,14 @@ class Order {
 
   Order.fromJson(Map<String, dynamic> json) {
     if (json == null) return;
-    if (json['id'] == null) {
-      id = null;
-    } else {
-      id = json['id'];
-    }
-    if (json['petId'] == null) {
-      petId = null;
-    } else {
-      petId = json['petId'];
-    }
-    if (json['quantity'] == null) {
-      quantity = null;
-    } else {
-      quantity = json['quantity'];
-    }
-    if (json['shipDate'] == null) {
-      shipDate = null;
-    } else {
-      shipDate = DateTime.parse(json['shipDate']);
-    }
-    if (json['status'] == null) {
-      status = null;
-    } else {
-      status = json['status'];
-    }
-    if (json['complete'] == null) {
-      complete = null;
-    } else {
-      complete = json['complete'];
-    }
+    id = json['id'];
+    petId = json['petId'];
+    quantity = json['quantity'];
+    shipDate = (json['shipDate'] == null) ?
+      null :
+      DateTime.parse(json['shipDate']);
+    status = json['status'];
+    complete = json['complete'];
   }
 
   Map<String, dynamic> toJson() {

samples/client/petstore/dart/flutter_petstore/openapi/lib/model/pet.dart

@@ -2,17 +2,17 @@ part of openapi.api;
 
 class Pet {
 
-  int id = null;
+    int id = null;
 
-  Category category = null;
+    Category category = null;
 
-  String name = null;
+    String name = null;
 
-  List<String> photoUrls = [];
+    List<String> photoUrls = [];
 
-  List<Tag> tags = [];
+    List<Tag> tags = [];
   /* pet status in the store */
-  String status = null;
+    String status = null;
   //enum statusEnum {  available,  pending,  sold,  };{
   Pet();
 
@@ -23,36 +23,18 @@ class Pet {
 
   Pet.fromJson(Map<String, dynamic> json) {
     if (json == null) return;
-    if (json['id'] == null) {
-      id = null;
-    } else {
-      id = json['id'];
-    }
-    if (json['category'] == null) {
-      category = null;
-    } else {
-      category = new Category.fromJson(json['category']);
-    }
-    if (json['name'] == null) {
-      name = null;
-    } else {
-      name = json['name'];
-    }
-    if (json['photoUrls'] == null) {
-      photoUrls = null;
-    } else {
-      photoUrls = (json['photoUrls'] as List).map((item) => item as String).toList();
-    }
-    if (json['tags'] == null) {
-      tags = null;
-    } else {
-      tags = Tag.listFromJson(json['tags']);
-    }
-    if (json['status'] == null) {
-      status = null;
-    } else {
-      status = json['status'];
-    }
+    id = json['id'];
+    category = (json['category'] == null) ?
+      null :
+      Category.fromJson(json['category']);
+    name = json['name'];
+    photoUrls = (json['photoUrls'] == null) ?
+      null :
+      (json['photoUrls'] as List).cast<String>();
+    tags = (json['tags'] == null) ?
+      null :
+      Tag.listFromJson(json['tags']);
+    status = json['status'];
   }
 
   Map<String, dynamic> toJson() {

samples/client/petstore/dart/flutter_petstore/openapi/lib/model/tag.dart

@@ -2,9 +2,9 @@ part of openapi.api;
 
 class Tag {
 
-  int id = null;
+    int id = null;
 
-  String name = null;
+    String name = null;
   Tag();
 
   @override
@@ -14,16 +14,8 @@ class Tag {
 
   Tag.fromJson(Map<String, dynamic> json) {
     if (json == null) return;
-    if (json['id'] == null) {
-      id = null;
-    } else {
-      id = json['id'];
-    }
-    if (json['name'] == null) {
-      name = null;
-    } else {
-      name = json['name'];
-    }
+    id = json['id'];
+    name = json['name'];
   }
 
   Map<String, dynamic> toJson() {