import { optional } from "https://deno.land/x/fuzzy_octo_guacamole@v5.0.1/patterns.ts";
P.optional(subpattern)
takes a sub pattern and returns a pattern which matches if the
key is undefined or if it is defined and the sub pattern matches its value.
Type Parameters
p extends unknown extends input ? UnknownPattern : Pattern<input>
Parameters
pattern: p