!undefined = true
!!undefined = false
!!!undefined = true

!false = true
!!false = false
!!!false = true

!true = false
!!true = true
!!!true = false

when using isEmailAvailable (positive) in correlation with exists (positive) make sure that the outcome is a positive return (and not an inverted)
inverted value required, double exclamation mark just casts as boolean
Merge pull request #279 from vincentbriglia/master

isEmailAvailable returns inverted value