CS8602 error stopping me from running Minimal API image uploader

I am trying to build an image uploader in a .NET 6 Minimal API. I believe that i have all the proper components but I am utterly confused on the problem that I am having. One specific line in the code has a CS8602 error stopping me from running the code.

app.MapPost("/submit-form", async (HttpContext context) =>
{
    var form = await context.Request.ReadFormAsync();
    var title = form["imageTitle"];
    var file = form.Files["imageFile"];

    // Perform validation checks
    if (string.IsNullOrEmpty(title))
    {
        context.Response.StatusCode = 400; // Bad Request
        await context.Response.WriteAsync("Image title is required.");
        return;
    }

    if (file == null || file.Length == 0)
    {
        context.Response.StatusCode = 400; // Bad Request
        await context.Response.WriteAsync("No image file uploaded.");
        return;
    }

    var allowedExtensions = new[] { ".jpeg", ".jpg", ".png", ".gif" };
    var fileExtension = Path.GetExtension(file.FileName);

    if (!allowedExtensions.Contains(fileExtension.ToLower()))
    {
        context.Response.StatusCode = 400; // Bad Request
        await context.Response.WriteAsync("Invalid file format. Accepted formats: JPEG, PNG, GIF.");
        return;
    }

    // If validation passes, continue with further actions
    // Generate unique ID for the image
    var imageId = Guid.NewGuid().ToString();

    // Store image information
    var imageInfo = new
    {
        ImageId = imageId,
        Title = title,
        file.FileName
    };

    // Serialize image information to JSON
    var json = JsonSerializer.Serialize(imageInfo);

    // Store JSON data in a file on disk
    var filePath = Path.Combine(Directory.GetCurrentDirectory(), "images", $"{imageId}.json");
    await File.WriteAllTextAsync(filePath, json);

    // Redirect to the page with the unique ID
    var redirectUrl = $"/picture/{imageId}";
    context.Response.Redirect(redirectUrl);
});

That is the first MapPost code block.

app.MapGet("/picture/{id}", async (HttpContext context) =>
{
    var imageId = context.Request.RouteValues["id"] as string;
    var filePath = Path.Combine(Directory.GetCurrentDirectory(), "images", $"{imageId}.json");

    if (!File.Exists(filePath))
    {
        context.Response.StatusCode = 404; // Not Found
        await context.Response.WriteAsync("Image not found.");
        return;
    }

    // Read the JSON data from the file
    var json = await File.ReadAllTextAsync(filePath);

    // Deserialize the JSON data to retrieve the image information
    var imageInfo = JsonSerializer.Deserialize<Dictionary<string, object>>(json);

    // Get the title from imageInfo dictionary
    string title;
    if (imageInfo.TryGetValue("Title", out var titleObj) && titleObj is string)
    {
        title = (string)titleObj;
    }
    else
    {
        title = string.Empty;
    }

    // Get the file name from imageInfo dictionary
    string fileName;
    if (imageInfo.TryGetValue("FileName", out var fileNameObj) && fileNameObj is string)
    {
        fileName = (string)fileNameObj;
    }
    else
    {
        fileName = string.Empty;
    }

    // Render a page that displays the image title and the image itself
    await context.Response.WriteAsync($"<h1>{title}</h1>");
    await context.Response.WriteAsync($"<img src=\"/images/{imageInfo["FileName"]}\" alt=\"{title}\">");
});

app.Run();

The error is happening just above the bottom of the code. in the second if statement,

if (imageInfo.TryGetValue("Title", out var titleObj) && titleObj is string)
    {
        title = (string)titleObj;
    }
    else
    {
        title = string.Empty;
    }

imageInfo is creating the error is dereference of a possibly null reference