I'm stucking with this issue:
I use in fomrs the calendar form field, MySQL database field for this is set to DATE and defaults to 0000-00-00
Form field definition in xml uses 

```
format="%Y-%m-%d"
default="0000-00-00"

```

On the frontend always appears 1970-01-01 instead of an empty field.
I searched the net but can't found a solution how to get an empty field if there is the zero in database. Can anyoune help me out?