We went ahead and did a quick roll for you on this, which you passed — grats!

The lamp retrieving party will successfully dispatch the Umber Hulk and claim the lamp for themselves. Unfortunately, goblins remain morons, so there isn't really anything particularly special about it at a first glance.

It is, however, filled with an oil that, should someone decide to douse themselves in it, will repel exactly one hit from an elemental magic spell or a magic item. That might come in handy later.