Find a blank image(.jpg) and store it in a folder. When you have null value in your Database then convert the blank image to byte array and send it to client.
byte[] testbyte = System.IO.File.ReadAllBytes("filepath");
if (v != null)
{
photo = testbyte;
return File(photo, "image/jpeg");
}
Instead of showing wrong image you can show blank image which will represent image is not available.