insert into: NULL in date column

A table has this column definition:

next_contact date DEFAULT '2020-11-06'
                CONSTRAINT valid_next_date
                CHECK (next_contact >= CURRENT_DATE),

(and I don't know that it needs a default).

In an input statement that column is left empty ('') when there's no defined
date. When I try to input that table I get a format error:

psql:activities.sql:2: ERROR:  invalid input syntax for type date: ""
LINE 2: ...reaction they''ve experienced environmental issues.','','');
                                                                 ^
and my web research has not shown me my error. Removing the check constraint
does not eliminate that error.

Please show me what I've done incorrectly.

TIA,

Rich