dfdl:nilKind 'literalValue' when the nil value contains delimiter characters

There is no code to escapify the contents of the literalValue nil value during unparsing.

So if this nil value happens to contain a delimiter character, and the lengthKind is delimited, then nothing will escape the delimiter that is part of the nil value, and so we will not be able to parse the data again.

An alternative to fixing this is just SDE, but since initiators/terminators/separators can come from runtime-valued expressions, a simple static check to rule this out isn't comprehensive but might be practical.