public static FieldUpdate createClearField(Field field) {
        return new FieldUpdate(field, ValueUpdate.createClear());
    }
Creates a new field update that clears the field. This operation removes the value/field completely.

@param field the Field to clear
@return a FieldUpdate specifying the clearing
@see com.yahoo.document.update.FieldUpdate#createClear(Field)
document/src/main/java/com/yahoo/document/update/FieldUpdate.java