Fix .reset() to correctly handle falsy default values

[kamontat]

Problem

Currently condition to use whether default value or undefined, is not accuracy.

if (value) {

}

The if condition with plain object in condition field will return false on falsy value including zero number (0), empty string (""), and false value of boolean (false). which on this case it might be actual default value.

Solution

So I create new function to help checking existing of variable which will check only not undefined and not null value