Oracle 如何根据对象类型填充表类型

CREATE OR REPLACE TYPE T1_OBJ AS OBJECT
(field1 VARCHAR2(10),
 field2 INTEGER);
 
CREATE OR REPLACE TYPE T1_TAB AS TABLE OF T1_OBJ;

DECLARE
  v_t1 T1_TAB;
BEGIN
  v_t1 := T1_TAB('Hernan',NULL);
END;

now, for some reason, if i put all null values, it works

DECLARE
  v_t1 T1_TAB;
BEGIN
  v_t1 := T1_TAB(NULL,NULL);
END;

SQL> CREATE OR REPLACE TYPE T1_OBJ AS OBJECT
  2  (field1 VARCHAR2(10),
  3   field2 INTEGER);
  4  /

Type created.

SQL>
SQL> CREATE OR REPLACE TYPE T1_TAB AS TABLE OF T1_OBJ;
  2  /

Type created.

SQL>
SQL> DECLARE
  2    v_t1 T1_TAB;
  3  BEGIN
  4    v_t1 := T1_TAB('Hernan',NULL);
  5  END;
  6  /
  v_t1 := T1_TAB('Hernan',NULL);
          *
ERROR at line 4:
ORA-06550: line 4, column 11:
PLS-00306: wrong number or types of arguments in call to 'T1_TAB'
ORA-06550: line 4, column 3:
PL/SQL: Statement ignored


SQL>
SQL>
SQL> DECLARE
  2    v_t1 T1_TAB;
  3  BEGIN
  4    v_t1 := T1_TAB(T1_OBJ('Hernan',NULL));
  5  END;
  6  /

PL/SQL procedure successfully completed.

SQL> DECLARE
  2    v_t1 T1_TAB;
  3  BEGIN
  4    v_t1 := T1_TAB(
  5                T1_OBJ('Hernan',NULL),
  6                T1_OBJ('Connor',5),
  7                T1_OBJ('Mike',10),
  8                T1_OBJ('Susie',NULL)
  9                );
 10  END;
 11  /

PL/SQL procedure successfully completed.