9cd8bc03_PL_SQL___Exceptions__Description
[Exception] COLLECTION_IS_NULL [Oracle Error] 06531 [SQLCODE] -6531 [Description] 
It is raised when a program attempts to apply collection methods other than EXISTS to an uninitialized nested table or varray, or the program attempts to assign values to the elements of an uninitialized nested table or varray.
PL/SQL - Exceptions
Description