Setting database field type Text to required should allow input of a single char "zero" value

Unable to use Number field type to store zero value when set to "required" (see MDL 53402), I tried to use a Text field type to input a single zero character, but could not, as both field types (Number and Text) use the same base data_field_base::notemptyfield() with empty value validation using "!empty($value)"

As with MDL-53402, suggesting to use isset($value) instead of !empty($value).