This service specifies a combo box which is data-aware, and can be bound to a database field.
Like most other data aware controls, such a combo box will display the actual content
of the field it is bound to. In addition, as a combo box contains a list where the user
can choose items to fill into the control, this list can be filled with different data from
a database, too.
determines if an empty text should be treated as a NULL value.
When the user enters text into a combo box, and after this, the control
content is to be committed into the database field the control is bound to,
a decision must be made how to deal with empty strings.
This is controlled by ConvertEmptyToNull.
If the property is set to true, and an empty text is to be commited, this is
converted into NULL, else it is written as empty string.
Note: A value of ::com::sun::star::form::ListSourceType::VALUELIST
is not valid for a combo box. It won't be rejected when setting it, but controls will usually ignore it
and leave the list empty.
