Blazor Component Reference Null on First Render

in my case it's solved by initialize the object

EX: private TabSet tabSet = new TabSet();

In first render, component is rendered. After first render, referent object is refer to component. So, at first time, ref of component is null(not ref). For more detail, document of blazor is detail issue in here

The tabSet variable is only populated after the component is rendered and its output includes the TabSet element. Until that point, there's nothing to reference. To manipulate components references after the component has finished rendering, use the OnAfterRenderAsync or OnAfterRender methods.

As Dani Herrera pointed out in the comments this may be due to the component being withing an if/else statement and indeed it was. Previously I had the component hidden if an object was null:

@if(Account != null)
{
    <TabSet @ref="tabSet">
     ...
    </TabSet>
}

I left this out for brevity and made the incorrect assumption that the issue was not the conditional. I was very wrong as on first render the object is null and therefore the component does not exist! So be careful out there. I resolved it by moving my conditionals to the sections within the component:

<TabSet @ref="tabSet">
    @if(Account != null)
    {
        <Tab>
         ...
        </Tab>
        <Tab>
         ...
        </Tab>
    }
</TabSet>