Is there any way to edit a table with null values inside the object?

example:

User object

UserId = 5
UserName = null; (do not change)
UserPhotoName = "bla.jpg"

now when i send this over to hibernate for editing, it will set the userName to null in the database, but it should just change the UserPhoto to the "bla.jpg" and dont do anything else.
Is there any way to prevent this and let it ignore the null values?

Thanks