SqlNullValueException: Data is Null. This method or property cannot be called on Null values.

When you have fields in a table that may contain null values, it's better to clarify this in your .NET Core model.

For example, you can denote nullable fields using the ? character, like so:

public int? RefID { get; set; }        

However, when I ran my program, it showed an error due to many fields being null. I resolved this issue by adding the following lines to the <PropertyGroup> in the project file:

<PropertyGroup>
    <Nullable>warnings</Nullable>
</PropertyGroup>        

This modification configures how the compiler handles nullability, helping to prevent errors related to null handling in .NET Core projects.