Simple Q&A D&D 4e Thread 3

[Vhaidara]

A63
Per the rules on extra damage

Many powers and other effects grant the ability to deal extra damage. Extra damage is always in addition to other damage and is of the same type or types as that damage, unless otherwise noted. Because of this rule, an effect that deals no damage cannot deal extra damage. However, a power doesn't necessarily have to hit a target to deal extra damage—it needs only to deal damage to the target.

(emphasis mine)

You need to deal damage to deal extra damage.
Rules Compendium 233