I've got a compiled project running as a scheduled task (it automatically sends out a newsletter to a subscriber list) that was working on DNN 5.4 but fails now at v6 and v6.1.5. The message is not very helpful... Can anyone shed any light on changes that might mean input into a Regex.Replace would be valid in v5.4 but not v6? Or is it that somewhere (and there's a few places as there's a lot of data gathered for the email) something that was returning data is now returning null?

AssemblyVersion: 6.1.5
PortalID: -1
PortalName:
UserID: -1
UserName:
ActiveTabID: -1
ActiveTabName:
RawURL:
AbsoluteURL:
AbsoluteURLReferrer:
UserAgent:
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: f81c2192-7b37-4403-886b-06edb230180c
InnerException: Value cannot be null. Parameter name: input
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: System.Text.RegularExpressions.Regex.Replace
StackTrace:Message: System.ArgumentNullException: Value cannot be null. Parameter name: input at System.Text.RegularExpressions.Regex.Replace(String input, String replacement) at Context.EventNewsletter.NewsletterScheduler.DoWork()