Handle null value for App Version

[monty241]

EPPlus usage

Commercial use (I have a commercial license)

Environment

Windows, Linux

Epplus version

8.5.0.0.0

Spreadsheet application

Excel

Description

Suggestion to allow setting AppVersion value to null in OfficeProperties.cs, now it fails with a NullReferenceException:

    public string AppVersion
    {
        ....
        set
        {
            string[] array = value.Split('.');
            ....
        }
    }