ZF-5051: Several methods have to be reimplemented in the file element to prevent unintentional uploading
Several methods in the parent element class make use of getValue().
As this method was implemented into the file element to allow simpler uploading, all other methods which make use of getValue within the parent class have to be implemented or overwritten in the file element.
Otherwise the file would be uploaded when it's not wished.
The following classes make use of getValue(): _getErrorMessages markAsError addError