Access WithMessage input from Validator

Consider the validator below:

public class SingleRuleWithMessageValidator : AbstractValidator<Person>
   {
   	public SingleRuleWithMessageValidator()
   	{
   		RuleFor(p => p.FirstName).NotEmpty().WithMessage("Specify a first name");
   	}
   }

Having extracted the NotEmptyValidator I was hoping to see the value of WithMessage within the exposed ErrorMessageSource, however the debugger shows this to be be null

Is there a way to retrieve the value of WithMessage?

[erendrake]

looking at this file https://github.com/JeremySkinner/FluentValidation/blob/master/src/FluentValidation/Resources/StaticStringSource.cs

it looks like you could call ErrorMessageSource.GetString(null); and it would give you the message? this wont work for all of the overrides of IStringSource but it does for the StaticStringSource

[JeremySkinner]

The ErrorMessageSource is simply a way of getting a raw string from one of several locations (could be a constant value, could be from a localization resource, or from a database etc). Calling GetString always returns the original, unaltered string (this is true for StaticStringSource - LazyStringSource could of course be doing any kind of manipulation of the string first) .

Filling in the placeholders requires contextual information about the object being validated, so can only happen during a call to Validate (specifically, the PropertyValidator class’s Validate method calls into the MessageFormatter to construct the final message). When calling GetString outside of this process, the information to fill in the placeholders simply isn’t available.