How to fix Null Reference Exception when adding a file to database(SQL Server)

I want store image in sql server I am using dot net web api, at the add method i get NUllReferenceException how to solve??

I am a begginer in webapi

This is the Code i have written

public async Task Upload(IFormFile file) { try {

        var uploadsFolderPath=Path.Combine(host.WebRootPath, "uploads");
        if (!Directory.Exists(uploadsFolderPath))
            Directory.CreateDirectory(uploadsFolderPath);


        var fileName= Guid.NewGuid().ToString() + Path.GetExtension(file.FileName);
        var filePath = Path.Combine(uploadsFolderPath, fileName);


        using (var stream = new FileStream(filePath, FileMode.Create))
        {
           await file.CopyToAsync(stream);
        }

        var photo = new Photo { FileName = fileName };
        photoContext.vehiclePhoto.Add(photo); // NullReferenceException
        await photoContext.SaveChangesAsync();

        return Ok(photo);

        }
        catch
        {
            return BadRequest();
        }