public static interface UniqueAttributeNameValidator.FieldProvider
Maps a Attrib/CompMember to a certain Vaadin field value. We need this, because we need the possibility to validate
the uniqueness of the Atrrib's/CompMember's aliases. While editing the final alias has not yet been written to the underlying
bean and therefore need to be considered by the name provider. This field is optional and may be empty, but not null.
For example at the initial validation phase the map may be empty, but while validating the input of the alias
of an Attribute in the Attributes tables the map should not be empty.