Don't update value with directive when mask is not defined.

[GaborTorma]

I would like to use your directives for a schema generadted form. In this case a v-facade directive always added to the attributes, but a lots of case it is empty.
Now Update runs with empty mask and modify the value.
Some special case the value is not string, but facade convert it and destroy the object.

Please check config.mask value exists also in directive, like masker

Thanx for your awsome job!