public DateTimeFormatterBuilder appendOptional (DateTimeFormatter formatter)
Appends a formatter to the builder which will optionally format/parse.
This method has the same effect as appending each of the constituent
parts directly to this builder surrounded by an
The formatter will format if data is available for all the fields contained within it.
The formatter will parse if the string matches, otherwise no error is returned.
| || the formatter to add, not null|
Returns: this, for chaining, not null