What is the error of this Blazor EditForm?

I tried to follow the instruction of creating form from youtube channel like those:https://www.youtube.com/watch?v=zfqQ_fhmPOQorhttps://www.youtube.com/watch?v=40njRXr6eUoor I even tried a very simple code like this

<EditForm Model="@author" OnValidSubmit="SaveAuthor"><p><label></label><InputText id="FirstName" @bind-Value="author.FirstName"/></p></EditForm>

Here is my github link for the code sample https://github.com/maxrena/BlazorServerApp.gitIt still returns the error like this Please help me with it.