According to my test, it works for envelope and convex hull and not for boundary, which seems "ok" to me :

-envelope of a point is the point itself

-convex hull of a point is the point itself

-boundary of a point is the empty set (see ogc and C2 point in http://tsusiatsoftware.net/jts/jts-faq/jts-faq.html\). OpenJUMP does not produce a feature with empty geometry in this case which seems fine to me, but which could be discussed...

Can you give a test case of what does not work for you

Michaël