Specialized class that wraps a single-valued non-null primary or secondary identifier attribute.
The intended use is in method parameters and internal data structures where it ensures the requirements on
the identifiers being passed on or stored.
Show the content of the object intended for diagnostics. This method is supposed
to append a compact, human-readable output in a single line. Unlike toString() method,
there is no requirement to identify the actual class or type of the object.
It is assumed that the class/type will be obvious from the context in which the
output is used.
This may be quite courageous. But (especially) ConnId requires String values of identifiers. So, this is the place
to change the way non-String values are to be handled.