The javadoc of the method Adjusters.dayOfWeekInMonth says:
Throws:
IllegalArgumentException - if the ordinal is invalid

Even though it also states:

The ordinal number of weeks is not validated and is interpreted leniently according to this algorithm.

and:

Parameters:
ordinal - the week within the month, unbound but typically from -5 to 5

I guess the @throws tag is a leftover that should be removed?

Kind regards, Anthony