ORA-02436: 在 CHECK 约束中错误地指定了日期或系统变量

这是我创建的表：

 CREATE TABLE Ticket_Type
 (
  t_type_id  NUMBER(1) PRIMARY KEY,
  CONSTRAINT check_t_type_id CHECK(t_type_id  > 0),
  t_type VARCHAR(20) NOT NULL,
  t_type_price NUMBER(4,2) NOT NULL,
  CONSTRAINT check_t_type_price CHECK(t_type_price > 0),
  t_type_start_date DATE NOT NULL,
  t_type_end_date DATE,
  CONSTRAINT check_t_type_end_date CHECK((t_type_end_date = NULL) OR (t_type_end_date >= t_type_start_date)),
  CONSTRAINT unique_t_type_t_type_start_date UNIQUE(t_type,t_type_start_date)
  );

我尝试创建此表，但收到以下错误消息：

Error report -
ORA-02436: date or system variable wrongly specified in CHECK constraint
02436. 00000 -  "date or system variable wrongly specified in CHECK constraint"
*Cause:    An attempt was made to use a date constant or system variable,
           such as USER, in a check constraint that was not completely
           specified in a CREATE TABLE or ALTER TABLE statement.  For
           example, a date was specified without the century.
*Action:   Completely specify the date constant or system variable.
           Setting the event 10149 allows constraints like "a1 > '10-MAY-96'",
           which a bug permitted to be created before version 8.

我无法弄清楚我犯的错误在哪里。

我正在使用 Oracle 版本 12c SQL Developer。