Maps undefined / null to empty string (fixes #435 and #448) (#449)
Maps undefined / null to empty string (fixes #435 and #448) (#449)

Mirrors the behaviour of Angular's DefaultValueAccessor (https://github.com/angular/angular/blob/2.4.8/modules/%40angular/forms/src/directives/default_value_accessor.ts#L46-L47)
text-mask/text-mask,text-mask/text-mask,CrisDan1905/text-mask,text-mask/text-mask,CrisDan1905/text-mask,CrisDan1905/text-mask,text-mask/text-mask,CrisDan1905/text-mask