Getting an "Object reference not set to an instance of an object." error in a simple Blazor app. What am I doing wrong?

Question

I'm getting the following error. From a simple all records call from my API.

crit: Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100]
  Unhandled exception rendering component: Object reference not set to an instance of an object.
System.NullReferenceException: Object reference not set to an instance of an object.
  at MusicManager.Client.Pages.Themes.BuildRenderTree(RenderTreeBuilder __builder) in
E:\Projects\marklalich\MusicManager\MusicManager\Client\Pages\Themes.razor:line 7
  at Microsoft.AspNetCore.Components.ComponentBase.<.ctor>b__6_0(RenderTreeBuilder builder)
  at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder
  batchBuilder, RenderFragment renderFragment, Exception& renderFragmentException)

Here's the code, what am I doing wrong?

@page "/themes"
@inject IThemeService ThemeService

<div class="container mt-3">
    <h2>Themes</h2>
    <p>asfgasfgasdfgasdfg</p>
    @if (ThemeService.Themes.Count == 0) <== this is the line the error is referencing
    {
        <span>Loading Themes...</span>
    }
    else
    {
        <table class="table table-striped">
            <thead>
                <tr>
                    <th>Title</th>
                </tr>
            </thead>
            <tbody>
                @foreach (var theme in ThemeService.Themes)
                {
                    <tr>
                        <td>@theme.Title</td>
                    </tr>
                }
            </tbody>
        </table>
    }
</div>

@code {
    protected override async Task OnInitializedAsync()
    {
        await ThemeService.GetThemes();
    }
}

Answer 1

The component first renders when

await ThemeService.GetThemes();

yields.

At this point I'm guessing ThemeService.Themes is null so there's no Themes to count:

@if (ThemeService.Themes.Count == 0)

So you need to make a null check:

@if (ThemeService.Themes is null)

Check the FetchData page.