You use the IS EMPTY operator to check if a nested table doesn't contain elements. The following procedure, is_empty_example(), illustrates the use of IS EMPTY:
SQL>
SQL> CREATE OR REPLACE PROCEDURE is_empty_example AS
2 TYPE nestedTableType IS TABLE OF VARCHAR2(10);
3 myTable1 nestedTableType;
4 result BOOLEAN;
5 BEGIN
6 myTable1 := nestedTableType('F', 'G', 'S');
7 result := myTable1 IS EMPTY;
8 IF result THEN
9 DBMS_OUTPUT.PUT_LINE('Nested table is empty');
10 ELSE
11 DBMS_OUTPUT.PUT_LINE('Nested table contains elements');
12 END IF;
13 END is_empty_example;
14 /
Procedure created.
SQL> CALL is_empty_example();
Nested table contains elements
Call completed.
SQL>