1、Iterable<E>增加扩展函数 isNullOrEmpty

lib/common/extension.dart

 import 'package:flutter/widgets.dart';
 
 /// 扩展函数 Iterable
-extension IterableExt<E> on Iterable<E> {
+extension IterableExt<E> on Iterable<E>? {
   // 获取元素
   E? getElement(int? index) {
-    if (index == null || index >= length || index < 0) {
+    if (this == null || index == null || index >= this!.length || index < 0) {
       return null;
     }
     int elementIndex = 0;
-    for (E element in this) {
+    for (E element in this!) {
       if (index == elementIndex) return element;
       elementIndex++;
     }
     return null;
   }
 
-  Iterable<T> mapIndexed<T>(T Function(E e, int i) f) {
+  Iterable<T>? mapIndexed<T>(T Function(E e, int i) f) {
     var i = 0;
-    return map((e) => f(e, i++));
+    return this?.map((e) => f(e, i++));
+  }
+
+  bool isNullOrEmpty() {
+    return this == null || this!.isEmpty;
   }
 }