If you are trying to read some nullable data from the database, but your type is not nullable you can get this error.
If MyInt is nullable in the database and you have this entity:

public class MyEntity
{
    public int Id { get; set; }
    public int MyInt { get; set; }
}

You will get the exception: System.Data.SqlTypes.SqlNullValueException: 'Data is Null. This method or property cannot be called on Null values.'
To fix this, just change the type of your MyInt property to Nullable<int> or int?:

public class MyEntity
{
    public int Id { get; set; }
    public int?MyInt { get; set; }
}