ProjectMethod: add missing comment
Fix missing javadoc links

The interface called Map used to be called FunctionalMap.
Fix javadoc

You cannot use '<' or '>' in javadoc because those are special HTML
characters. They must be escaped in one of two ways; either:

1) &lt; and &gt; or
2) via the {@code ...} syntax.

We use the latter here, for readability.
MapII2II: fix bug in isValid method