c# - 使用c#找不到表

Question

我试图更改表格中特定单元格的值，但出现错误，任何人都可以看到问题所在：

测试WebTable.IWebTableTests.testIWebTableTests失败：System.NullReferenceException : Object reference not set to an instance of an object. WebTableTests.cs(37,0): at WebTable.IWebTableTests.testIWebTableTests()

<div class="cart-info">
   <table border="1">
     <thead>
         <tr>
            <td class="name">Product Name</td>
            <td class="model">Model</td>
            <td class="quantity">Quantity</td>
            <td class="price">Unit Price</td>
            <td class="total">Total</td>
         </tr>
     </thead>
    <tbody>
   </table>
</div>

和：

IWebElement table = driver.FindElement(By.CssSelector(".cart-info>table"));
ReadOnlyCollection<IWebElement> allRows = table.FindElements(By.TagName("tr"));
ReadOnlyCollection<IWebElement> allCols = table.FindElements(By.TagName("td"));

//Verify that it has three rows
Assert.AreEqual(3, allRows.Count);
//Verify that it has six columns
Assert.AreEqual(5, allCols.Count);
//Verify that specified value exists in second cell of third row


Assert.AreEqual("iPhone", allRows[3].FindElements(By.TagName("td"))[1].Text);
//Get in cell editor and enter some value 

string cellValue = allRows[3].FindElements(By.TagName("td"))[3].Text;
IWebElement cellEdit = allRows[3].FindElements(By.TagName("td"))[3];
cellEdit.Clear();
cellEdit.SendKeys("2");
string aftercellValue = allRows[3].FindElements(By.TagName("td"))[3].Text;